Huge example in season 3 of Angel. Wesley translates a prophecy that Angel will kill his son, Connor. Instead of telling Angel (or Gunn, or Fred), Wesley kidnaps Connor and loses him to Angel's archenemy, which results in Connor being raised in a Hell dimension and growing up to hate Angel fiercely. While the urge to protect baby Connor is understandable, everyone gives Wesley a hard time about not just telling them what was going on in the first place so they could help him make a better decision. On top of it all, it turns out the prophecy was a fake the whole time, meaning Wesley's actions were All for Nothing.
In Babylon 5, the whole Human/Minbari war starts because of this, mostly because they don't know each-others language or cultural traditions.
To Minbari, it is common courtesy to show all your weapons to other soldiers, so they can see that you have nothing hidden and mean no treachery. Which on a warship means opening all gunports ready but leaving the weapons powered down. The humans noticed the first part and mistook a power spike for powering up the weapons (also, the Minbari sensors had accidentally jammed human jump drives and their stealth was keeping human scanners from getting a clear reading) and started firing in presumed self-defence, killing the Minbari's revered leader, resulting in them declaring holy war against the human race and making no attempt to communicate with the humans, neither to tell them the reason the Minbari are trying to kill them all, nor to get any explanation for the humans' actions. Ironically Dukhat, the Minbari leader, had ordered to close the gunports to avoid this in the exact same moment the Human commander ordered to open fire.
To make things even more tragic, it's possible the Minbari were powering weapons... To shoot at Soul Hunter ships that the human ships couldn't detect. That was when Dukhat ordered to close the gunports: Soul Hunters have the ability to sense when someone will die and, being hated and feared by everyone else, show up only when someone whose soul they deem worthy of preserving is about to die, leading Dukhat to realize the humans were about to mistake the open gunports for a hostile action and open fire, but he gave the order just as Jankowski, the human commander, was ordering to open fire. Anger at the "unprovoked" attack pushed the Grey Council, the Minbari government, to declare and announce a holy war to exterminate the humans, and by the time they realized it was not so unprovoked they couldn't take it back out of fear of losing their people's trust.
Interestingly, when a Minbari warship shows up at Babylon 5 showing all weapons as common courtesy, the warship's captain Neroon arrogantly refuses to explain himself; the more level-headed Minbari Ambassador Delenn goes to the bridge to enlighten the Bab 5 crew about this tradition and invite them to confirm that the weapons are not powered. Apparently, even ten years after the Earth-Minbari War, all the details of the misunderstanding that kicked it off are still not common knowledge in the Earth Alliance, due to the Minbari's poor communication skills. Also, Delenn probably could've warned the humans before the warship arrived.
Sheridan once mentions that the need for proper communication was the first thing he learned at the Academy.
In the In the Beginning TV movie, Sheridan even warns his superior not to send that particular commanding officer with a bad record of First Contact situations (such as something called the Omega Incident) to meet an ancient and powerful race, claiming he was impulsive. Had a less impulsive officer been in command, it's possible the whole war would've been averted. The superior officer unfortunately didn't listen, citing that Jankowski had been cleared of responsibility in the Omega Incident.
Later, Sheridan is sent to meet a friend of Delenn's who wants to open a back-channel of communications between humans and Minbari hosted by G'Kar. Unfortunately, Londo assumes that the Narns are scheming against the Centauri and sends a warship to attack the meeting. Sheridan, Franklin and G'Kar are the only survivors.
Much of the latter half of Battlestar Galactica, if not the entire series, could have been avoided if the humans and cylons had ever just sat down and compared notes, but even after the humans have cylon allies, they still don't even seem to consider sharing information with each other, despite all the half-information and lingering questions they all have about prophecies, the backstory, etc.
The last episode of Blake's 7 has Tarrant fall for Blakes bounty hunter act and tell Avon that Blake has betrayed them. Avon, who really should know Blake better than that, aims his gun at Blake, who, instead of explaining the truth coherently, just comes out with vague statements like "I set all this up!", all of which Avon misinterprets until he finally snaps and pumps Blake full of gunfire.
In Season Six, Riley neglects to tell Buffy he needs the demon he's just sent her after captured alive. His new wife criticizes him for it.
Faith's induction into the Scoobies helped to temper her lawless approach to slaying (which Buffy initially didn't know about). However, Buffy lied to her about Angel's resurrection, which allowed Gwendolyn Post to use this to turn Faith against the gang.
In Chicago P.D., Voight continually clashes with Violent Crimes, with their Lieutenant annoyed that Voight doesn't share information - to which Voight retorts that neither does Violent Crimes share any information with Intelligence. Both parties claim to leave voice messages for each other. Towards the end of the episode, Intelligence rolls up to an apartment where they believe a drug dealer is going to be killed... and Violent Crimes rolls up, telling Voight they're following up on the car belonging to some cartel hitmen, which was spotted at the apartment. It results in one Intelligence detective being shot in the neck, and pronounced dead on arrival.
When the producer of a local television mentions that there is room for only one more dancer (either Theo or Cockroach), Theo repeatedly insists on Cockroach going in. At first, Cockroach objects, because Theo had the tickets. Eventually, Cockroach accepts, causing Theo to become extremely bitter about it. He starts acting like a jerk around his family until Clair tells him that it was his own fault for being dishonest.
A few years later, Sondra has to forfeit a night out with Elvin and two friends, but she repeatedly insists that Elvin continue as originally planned. She thinks that Elvin will make a final objection, but he caves in and accepts. Later on, she gives Elvin the silent treatment until Clair puts the blame on Sondra for not expressing her true feelings.
In the Dad's Army episode "Ring Dem Bells" Wilson and Pike go into the Eight Bells pub with the platoon dressed as Nazis for a training video. Instead of just explaining to the barman what's going on, they cause widespread panic.
"The Mutants": If the Earth Administrator had just started his speech by saying he was granting Solos their independence, the whole plot would have been avoided and he'd have saved his own life.
"The Beast Below": It turns out that the Star Whalevolunteered to help save the UK by coming so they could build Starship UK on its back. Not being able to communicate this to the humans led to it being captured and tortured for 200 years, with people who protested against the torture being fed to it.
Drop Dead Diva: The entire romantic subplot of Season 5 could have been solved by Jane just explaining that Grayson kissed her without any provocation on her part to Owen rather than keeping it to herself and angsting over it until it was too late.
ER once had a Hispanic woman brought in showing mysterious symptoms. Susan talks with her husband and discovers that the patient is overdosing on medication. The directions said to take it "once a day", but she thought it meant "eleven a day". ("Once", pronounced on-say, is Spanish for eleven.) Despite them figuring out the problem, the patient still dies.
In the Ever Decreasing Circles episode "Manure", laid-back Paul Ryman is away at a Pro-Am golf tournament and asks his neighbour Martin Bryce to take a delivery of manure for him. However, Martin is busy obsessing over the fact that Paul's garden seems to be free of molehills, unlike his own, so when the tractor of manure arrives, he is standing in Paul's driveway when he tells the driver, "Well, I don't want it on my driveway, do I!? Put it on Mr. Ryman's!" The driver promptly dumps the manure in Martin's driveway.
The climax of the Firefly episode "The Message" has the intrepid crew under siege and almost certainly about to die at the hands of an overzealous cop hunting down Mal and Zoe's friend, Tracey. Shepherd Book hatches a plan: the first part is surrendering to the cop and telling him they're going to turn Tracey over to him. Tracey overhears this part of the plan and grabs a gun and fires at the crew, holds Kaylee hostage, refuses to put down his weapon when cornered, and finally is mortally wounded by Mal. It isn't until he lays dying that the plan is revealed to be to lure the corrupt cops into a trap and confront them with the fact that they're outside their jurisdiction. Tracey didn't ask if there was any more to the plan, and Mal never bothered explaining the plan after Tracey started shooting up the ship and took one of his crew hostage, meaning poor communication from both sides got Tracey killed.
Frasier often relied on the titular character, an eloquent, educated man who could often string together the most complicated of sentences, being rendered incoherent when a simple explanation could extricate him from a difficult situation. One episode played with this dynamic when Frasier's dad tried to return $40 that was mistakenly given to him by a bank's ATM. He patiently, articulately explains the situation in terms so clear even a child could understand...and the bank employees all misunderstand him and what he wants.
When Chandler attempts to masturbate and Monica (his wife) interrupts him. He quickly changes the channel to a show about sharks, and Monica presumes this means he finds sharks sexually stimulating.
The infamous break up between Ross and Rachel stems heavily from this trope. Had Rachel been more clear on what "being on a break" meant, Ross would not have misinterpreted it as a break up. Of course, a running joke in the later seasons was that her reasoning on this made sense only to her.
In "The One Where No One Proposes", after Joey finds a ring on the floor, Rachel accidentally thinks he is proposing to her and accepts. Instead of simply telling Rachel the truth about his "proposal", Joey spends most of the episode embarrassed about the misunderstanding and getting into awkward situations with Ross, who was actually the one who wanted to propose to Rachel.
The War of the Five Kings results at least partially from very poor communication between the Starks and the Lannisters when Catelyn arrests Tyrion with little evidence and without questioning him at all first. In addition, Cersei never even tries to explain to Ned Stark that she didn't actually kill Jon Arryn.
It is revealed in the Season 7 finale that Rhaegar Targaryen and Lyanna Stark really do fell in love with each other and secretly married in Dorne. While it did disproved the fact about Lyanna being kidnapped and raped by Rhaegar and confirmed that Jon Snow (or Aegon Targaryen) is the legitimate heir to the Iron Throne, the whole love affair still led to a civil war that affected several houses for a long run. Had Lyanna or Rhaegar told their families about it instead of running away together and eloping somewhere else, many deaths could have been prevented.
Tywin taught Tommen that a wise king listens to his advisers, however, Cersei and the small council made no effort to advise him on running the kingdom and refused to make him a part of their plans and affairs. So when Tommen attempted to confront the High Sparrow on his own, he found himself swayed by his charm and his platitudes and ended up allying the Crown with the Faith Militant. Now under the High Sparrow's guidance, Tommen makes new acts and decrees without consulting his mother or the small council.
Curiously Inverted in series 8. While other issues contributed as well Daenerys' Sanity Slippage is in part caused by increasing Paranoia as her advisors become aware of the secret of Jon's parentage and begin plotting against her.
In The Good Doctor Season 3 episode "45-Degree Angle", Dr. Shaun Murphy, the autistic protagonist, leads his first solo surgery and asks one of the nurses to hand him an instrument, but when the nurse hands him the requested instrument at the incorrect angle, he kicks her out of the operating room. Dr. Lim then orders Shaun to apologize to the nurse, which Shaun is hesitant to do, then tells him that he didn't do things right himself and that he needs to "make this right" without clariyfing to him exactly what she means. So instead, Shaun approaches the nurse while she's having lunch and tries to show her what she did wrong and how to hand him the instrument the correct way, which leads the nurse to storm off and later file a compliant against him, and Lim to sternly tell him off for not apologizing, even threatening to fire him if the incident or anything else of the kind happens again, and it's only at that moment that she gives him the information he needed earlier.
This is what kicks off the entire mess of Good Omens. The pregnant wife of an American diplomat is about to give bith in a convent where the nuns (working for Hell), plan to swap her child for the Antichrist that Crowley is going to deliver so he grows up in an influential political family as the first step to Armageddon. But then a couple called the Youngs show up, the wife also in labor and things get out of hand. When Crowley comes by, Mr. Young tells him "the birth" is happening in Room 3, meaning his wife but Crowley assumes that it's the American woman and takes the Antichrist to that room. Then, Sister Mary mistakes Mrs. Young for the diplomat's wife and makes the switch of that kid for the Antichrist. She and Sister Theresa then exchange winks which each totally mistake what the other is thinking and Mary not grasping she just gave the Antichrist to the wrong family. Then, some demons wipe out the entire convent before double-checking on things. Crowley and angel pal Aziraphale (not wanting the world to end) work together to try and keep the diplomat's son from going evil, unaware they're working on the wrong kid. Thus, these mistaken assumptions all pile up on each other and nearly end the entire world.
Scores of examples on Gossip Girl with the characters just failing to make the logical connection of talking rather than jump to the wrong conclusions.
The best example may be when Lilly visits Serena's school and hears some girls talk about how Serena has been having an affair with her teacher, Ben. Concerned, Lilly reports Ben to the school board, expecting them to just fire him and hush it up. Instead, they want Ben prosecuted for statutory rape. Wanting to spare Serena a trial, Lilly forges a statement from Serena on what Ben did and he goes to jail. This later causes Ben's sister, Juliet, to embark on a wild scheme of revenge on Serena that nearly ruins her. When Juliet snaps she's paying Serena back for ruining her brother, Serena cuts her off by saying she has no idea what Juliet is talking about. After Lilly is forced to confess what she did, Serena drops the bomb: The "rumors" were just that, Ben never laid a hand on her. Serena openly lampshades how Lilly didn't even bother asking her daughter if the rumors were true before destroying an innocent man's life.
Bruce goes looking for Reggie Payne at gun ranges based on Alfred's statement that he's probably holed up in "a shooting gallery". The more streetwise Selena explains the other meaning of the term (a place where people hole up to do drugs).
A lot more people would still be alive, and a lot less trouble gone to if Cobblepot could've just told Nygma that he's in love with him.
In Have Gun Will Travel, Paladin's business card can cause some confusion over his profession that can occasionally lead to rather unfortunate mix-ups. More often than not the confusion is resolved without anyone dying, but every now and then... This is actually what gets him started as a hero in the pilot, he was tricked into fighting a "notorious killer" who was actually also a good guy and ended up taking on the dead man's quest after learning the truth.
In episodes 2.09 and 2.10; Mohinder utterly failed to tell Overprotective Dad Noah that he didn't need Claire, just a pint of blood to save a life and stop a plague rather than kidnap her. Instead he made it seem like he had done a FaceHeel Turn and was going after this Overprotective Dad's daughter and bringing about the season's Tear Jerker episode.
Peter and Hiro ended up in a fight because neither was all too keen on examining why each was doing what they're doing by defending and attacking Adam respectively. And these are people who can stop time! Hiro and Peter could have had talked it out while sipping tea in Tokyo and come back with the whole thing handily resolved, were it not for "With great power goes all intelligence".
In the first episode of Volume Four, Claire overhears her father, Nathan, explaining to her grandmother, Angela, that he is sending government agents out to get Peter and Matt and that he wants to keep Claire home and out of this entire situation (Claire gets a free pass). So Claire, giving her grandmother a nice Death Glare, gets herself into the situation and calls Peter. Reasonable enough, right? She tells him government agents are after Matt ... then completely fails to mention they're after Peter too.
Several episodes actually are this trope. Any kind of small detail about the patient or their family members not revealed, generally ends with the patient having at least one near death experience.
An early episode revolved around a lacrosse player who got injured during a game. The answer to his problem stems from the kid actually being adopted and his biological mother not being vaccinated. This is entirely the parents' fault, as this fact was never revealed by them. Although the kid already knows.
How I Met Your Mother: There's an episode where Barney runs the New York City marathon without any prior training. He finally feels the effects while riding the subway a little later: his legs lock up and he can't stand. Eventually, a pregnant woman, an old lady and a little boy in crutches enter the crowded train and ask for his seat. Instead of just explaining that his legs don't work, he simply mutters, "I'm sorry. I can't." Now, New York being New York, it's possible no one would have believed him, but the explanation would have been better than the vague thing he actually did say.
In the Intelligence episode "Delta Force", Gabriel's old Delta Force friend Norris committed a series of political assassinations because his CIA handler somehow misinterpreted a very terse message from D.C. saying that the U.S. was in favor of Bolivian presidential candidate Javier Leon as "eliminate Javier Leon's competition".
Harm and Captain Reed in "Desert Son" do not get along, and Reed gives the bare minimum of assistance when Harm and Meg go to investigate the accident site. This plus one knocked over road sign nearly get Meg and Harm killed when they accidentally enter the Free Fire Zone.
In "Scimitar", Meg is not let in on the secret part of their mission and is left to improvise when she discovers that Harm is in danger.
Kamen Rider, any series under the writing of Toshiki Inoue tends to suffer from this.
Agito, Faiz, and Kiva all had near-identical situations: a member of the secondary castnote Ryo Ashihara/Gills, Yuji Kiba/Horse Orphenoch, and Keisuke Nago/IXA, respectively is friends with the main character while wrongly thinking that their Rider identity is evil because of some crime or deednote Ashihara believes Agito killed the woman he loved, Yuji believes Faiz is a pawn for Smart Brain, and Nago believes Kiva is an Omnicidal Maniac. The protagonist never thinks to reveal his identity in order to defuse the situation, which lets the tension build. In the end, everything is resolved peacefully when the secondary character learns the hero's identity by accident, since he knows that the hero is a good person and therefore realizes that his hatred of their Rider identity was misplaced.
There are a couple of minor tweaks to this formula. In Faiz, it's the fact that the Rider Belts get passed around like Halloween candy, and one character actively uses the Faiz Gear to try and sow discord because he hates both Takumi and Kiba. Kiva had an incident where Wataru half-admits it (Nago asks "Where did Kiva go?!" and Wataru wordlessly points at himself), but Nago just brushes it off as a bad joke; also, it's later revealed that there the Kiva who was active in the 1980s really was an Omnicidal Maniac (and Wataru is his Redeeming Replacement), so Nago's suspicions weren't completely unfounded.
Played with, but ultimately averted in Kamen Rider Blade. After spending almost the whole series fighting each other, all four Kamen Riders are finally united as a team during the last arc of the show. Logically, this is not desirable for the Big Bad, who sends out a monster capable of disguising itself as the Kamen Riders, tasking it with turning the Riders against each other. Luckily, the Riders realize the Big Bad is trying to invoke this trope.
It's played straight in Kamen Rider Drive, but not without some resistance and subverting. Despite all the good reasons to keep secrets, Shinnosuke has pointed out just how troublesome keeping things a secret is and even his superior felt the need to reveal who the Kamen Riders are. However, keep in mind that it's straight. Three of the major characters (The Mentor, The Rival, and the Tsundere) all have knowledge of a guy who isn't right in the head. However, their insistence on keeping secrets is what got said scientist to pass by undetected and eventually hijack the position of Big Bad.
In episode 15 of Kamen Rider Ex-Aid, Taiga and Hiiro learn that Emu is Patient Zero of the Bugster Virus, and seemingly attack him out of nowhere, believing that telling him the truth would make things worse. Their point is proven when Kuroto ends up revealing the truth to Emu, spiking his stress levels and worsening his disease.
An almost literal example happens in a Key & Peele sketch, where Jordan Peele's character sends a series of text messages to Keegan's character that were meant to be casual in tone but gets interpreted as dismissive to the point that an invitation to go hang out at a bar gets interpreted to a challenge to a fight. This leads to the latter storming into a bar with a nail-bat, only to find the former happily waiting for him (and thinking that the bat was meant as a gift).
A literal example in Killjoys as season three has them tangling with Hullens, specially created aliens in human form who heal quickly from injury. In "Attack the Rack", Dutch stages an assault on the RAC to expose the Hullens in their ranks to the human agents and have them fight back. She's looking in a room when attacked by Banyon, the recently appointed RAC boss. Naturally, Dutch believes she's a Hullen and they start fighting it out with Dutch stabbing Banyon in the side. To her shock, Banyon doesn't heal from it and Dutch realizes she's human. It turns out Banyon didn't know a thing about the Hullens and was just looking into what happened to missing agents. She assumed Dutch and her crew were somehow involved and that's why she was so hostile to them. Both women realize that they've been on the same side but mutual suspicion (and Dutch not wanting to reveal the Hullen threat until she was ready) caused this with Banyon dying of her wound.
Fans (and detractors) of Lost have commented on the characters' apparent inability to ask the right questions. In particular, they've had Juliet among them since her HeelFace Turn, but have not asked her any questions about the intentions or nature of the Others. This tendency was lampshaded in the season 4 episode "Cabin Fever," as Christian says to Locke, "So why don't you ask the one question that does matter?" Actually played for laughs early on, when Michael is incredulous when the others talk about polar bears, and a confused Charlie says "You didn't hear about the polar bear?"
So many problems on Merlin (2008) could have been solved instantly if Merlin wasn't almost pathologically secretive - and not just on his magical abilities (which he is justified in keeping to himself) but things such as traitors in Camelot and other characters getting magically brainwashed.
So much of the comedy of Modern Family relies on family members completely misunderstanding a situation which makes it more chaotic.
Phil realizes that Luke mistook a facial tink as a winking signal for him to ruin Claire's attempt to buy a shed. It also turns out Luke has been doing this thing a lot over the years.
Luke: You think Alex's cello set itself on fire?
A frequent bit is that between Gloria's bad English and Luke and Haley's dim-wittedness, miscommunication can abound over the smallest things.
Manny is a classic case of a child older than his years and enjoying a more cultured lifestyle and assumes almost everyone in his school is the same way. Thus, he won't grasp that trying to theme a dance to an obscure classic musician won't go over well.
There's also the way the various spouses will attempt to one-up each other and cause more chaos.
Really, it was all summed up in a rare bit of wisdom by Luke: "90 percent of your problems would be solved if you just talked to each other more."
Biggles: Are you gay? Algy: I should very well say so, old fruit! (Biggles shoots Algy)
In The Musketeers, when Athos has been forcibly dragged back to the lands he owns to see how badly they're doing without a lord, he says to his sister-in-law that "I should have signed the land over to you" before he left, but he would do so now. She immediately starts wearing her finery again and talking about what a wonderful thing he's done for her. And somehow, he doesn't realise that she thinks the land is going to be gifted to her personally, not a group "you" meaning "the tenants".
This is how Joel got off the Satellite of Love. Gypsy had caught a transmission from Deep 13 with Dr. Forrester and TV's Frank plotting to kill Mike Nelson, utterly sick of how he's marching around like he owns the place. Gypsy misinterprets this as them wanting to kill Joel and sets off to "save" Joel from the Mads. While she does save Joel, she doesn't save the other robots or herself and leads to Mike being the one stuck up there.
The Nova episode "The Spy Factory" accuses the NSA and CIA of this during the lead-up to 9/11, sitting on intelligence they had on al-Qa'ida rather than passing it along to the FBI so they could do something with it.
In "Trial by Fire", alien forces are hovering above the Earth, and have sent out a message to the world's leaders. The message, unfortunately, is unable to be deciphered, and the President of the US is presented with two options - Preemptive strike, or wait things out and hope they can translate the message. He eventually takes the Hawk approach and launches a nuclear warhead at the UFOs, which fails. As a retaliatory strike comes in, he's informed that they just cracked the code... by submerging the audio beneath water; it was a message of Peace. But what were you expecting? There's a reason that the trope Cruel Twist Ending was originally called Outer Limits Twist.
In "Summit", the Dregocian delegation's shuttle is destroyed in an ion storm as it approaches the planetoid where it was supposed to hold peace talks with the human delegation. The shuttle's last message accuses the humans of sabotaging it. The human and Dregocian motherships destroy each other in the chaos that follows. The human delegation detects both sides preparing for war and determine that they will come into firing range of each other's fleets in three hours. As their transmitter is damaged, the humans cannot alert either side that it was all a terrible misunderstanding.
In the early seasons, Alexis falls for the very quiet and introverted Mutt. They begin a romance, but his inability to communicate and her talkativeness kills their relationship.
David falls in love with Nice Guy Patrick, who generally expresses himself well. However, Patrick is sometimes reticent to reveal information that he feels will upset people. This leads to him not communicating his feelings to David early on and Stevie having to point out to David that he is in a Not a Date situation with Patrick. Also, Patrick neglects to tell David he was once engaged to a woman until the woman shows up in town looking to reunite with him. Later, David invites Patrick's parents to a Surprise Party only to discover Patrick hasn't come out to them. Thankfully, David learns to be understanding of this quirk of his boyfriend and they work things out.
An episode of Scrubs focused on the effects JD's insane hours at the hospital were having on his life. It manifested in particularly dramatic fashion on a date, where JD, upon looking at the incredibly gorgeous girl he was about to kiss, instead saw the hideous cancer patient he was treating earlier in the day. He mumbled something incoherent and walked away. The next day, when the girl asked him why he bailed, JD actually said nothing instead of explaining the situation. JD's narration even lampshaded the communication failure, and it was included in a trio of scenes where males proved utterly incapable of communication with their girlfriends.
In The Shannara Chronicles, mystic Allanon is told by his mentor Bremen that he will one day have a successor. Allanon is convinced this is Bandon and goes overboard in driving the young man to learn all the magic he can and prove himself. All this ends up doing is turning Bandon to darkness and to become a major threat. Badly injured, Allanon meets with the spirit of Bremen, who reveals his true successor is Mareth. Allanon lampshades that maybe so much trouble could have been avoided if Bremen had just used a gender pronoun to give a hint Allanon's successor would be a woman.
Happens so many times on Smallville, usually because the A.I. of Jor-El in the Fortress of Solitude is a total prick and insists on talking cryptically.
"Solitude": Brainiac infects Martha with a deadly kryptonian virus. Clark questions Jor-El, and all he says is that "I am sorry, my son. The wheel of fate has already been set in motion. Even you cannot alter destiny." This Is Wrong on So Many Levels.
"Lazarus": Jor-El warns Clark Kent that "a great darkness" is coming. Sure enough, Lex Luthor (actually his clone) returns. Clark defeats him and reports his success. Jor-El reveals that he doesn't really give a crap about Lex Luthor. The "great darkness" he was refering to was Darkseid, who arrives on Earth safely and unnoticed. To make this situation even worse, Jor-El just tells off Clark for the mistakes he made during the episode and shuts himself and the fortress down, without telling Clark anything about the actual threat.
Sons of Anarchy Gemma is upset because Tara wants to move away from Charming and take her kids (Gemma's grandkids) with her. Tara is under investigation and Gemma has used this threat to keep Tara in Charming. Suddenly, Gemma finds out Tara's charges have been dropped and Tara is free to go where she pleases. Gemma assumes this is because Tara made a deal to turn on Jax (Tara's husband, Gemma's son, and the leader of a less than legal motorcycle club). Without asking any questions, Gemma violently attacks Tara and brutally kills her to protect Jax, only to later find out that Tara's charges were dropped because Jax made a deal to get Tara's charges dropped. And everyone but Gemma knew that was the case.
Spock would literally rather die than have the problem explained to Starfleet Command. This is apparently true of all Vulcans at this point in history.
It's possible that Kirk could've explained things to Komack in a way that would've gotten him permission to go to Vulcan without letting too much slip. Kirk even had his Chief Medical Officer's statement that Spock would die if he didn't return to Vulcan, and didn't bother to mention it to the Admiral.
Poor communication also almost killed Kirk in this episode. Would it have hurt T'Pau to tell him that the fight was a death match before he signed up?
Superior Donuts has this almost happen when the shop introduces their new PB & J donuts.
Tush: Oh! I can't feel my face! Quick, are there peanuts in those donuts? Arthur: There's peanut butter. What did you think the "PB" stood for? Tush: Probably Bacon!
About half of the Winchester family drama could have been avoided if Sam and Dean simply told each other about their problems rather than insisting they're fine.
Castiel's slide into evil in Season 6 could have been avoided if he'd simply asked the Winchesters for help, and if the Winchesters hadn't blown off the civil war in heaven as somebody else's problem.
The final seal keeping Lucifer imprisoned could have remained intact if certain parties who wanted the Apocalypse to happen didn't do their best to make sure the Winchesters don't learn until it's too late that Lilith's purpose isn't to break the final seal, she is the seal and her purpose is to be slain by Sam, Lucifer's true vessel. It also doesn't help that Sam made the spectacularly poor decision to trust a demon and that Dean all but disowned Sam when he found out instead of reaching out to him. Bobby called Dean out on that.
And poor poor Kevin. If only Dean had bothered to tell him that Sam might be dangerous when he straight up asked. Maybe the man just didn't have enough reasons to wangst.
The show's Hypercompetent Sidekick Stiles Stilinski hangs a lampshade on this trope and states that a complete lack of communication is the main reason why all of the characters are having so many problems in season two. He points out that nobody trusts anyone else and the inability to effectively communicate between werewolves and humans was eventually going to get someone killed.
Also, most of the plot of the first five episodes in season one could have been skipped if Derek had just taken five minutes out of brooding and TOLD Scott he hadn't been the one to bite him.
Victoria Argent wasn't able to talk to Allison one last time before she kills herself (to stop from becoming a werewolf), so she is unable to tell her daughter what led to her death (that she tried to kill Scott and Derek bit her in Scott's defence). Then Scott doesn't tell Allison what happened either, because he doesn't want to damage Allison's memory of her mother. This allows Gerard to manipulate Allison by casting Derek in the worst light possible.
Gwen tries to keep her actual job in Torchwood secret from her boyfriend in the least helpful way. Despite Torchwood's ability to set up dummy companies, create false identities and twist the truth when the need be Gwen never uses any of this to give her boyfriend any reason to calm down about her job. Instead she is openly ambiguous about why she works such long hours and gets called away so often. Even her boss says she shouldn't let her personal life drift, but never makes any good suggestions to Gwen as to how to do so. This can get frustrating for the viewer because obviously some people on the police force know Gwen does something working for Torchwood, and people out in the world know Torchwood does something (The woman in the first episode of series 2 mutters "Bloody Torchwood" as they pass by.)
Rex gets aggravated by the tendency of Gwen and Jack to run off and try to handle things on their own instead of just asking for help. He lampshades this trope when Gwen receives a message through the special contact lenses that her family is being held hostage until she brings them Jack. Given the fact that the bad guys could only see whatever Gwen could see or receive a transcript of what was said while Gwen was looking at someone, she could easily have told Rex and Esther (and, you know, Jack, before kidnapping him what was going on without tipping her hand.
The Tribe: So many problems on the show stem from characters simply not explaining what they mean to each other or making assumptions based on incorrect/incomplete information.
In UFO, one episode has Foster being saved by an alien after he's injured. However, the explosion in which he was hurt also destroyed his communication device. He and the alien manage just fine, communicating with gestures, but once he's rescued, things don't work too well. Foster tries to tell his rescuers to save the alien, but they can't hear him. Finally, one of them gets the idea of pressing the faceplate of his spacesuit to Foster's. Foster tells him, "There's an alien. Help him - he's a friend." Unfortunately, the only word that gets through is "alien". They figure he's been attacked and shoot the alien, while Foster can't tell them to stop.
In the final season of Veep, Selina is trying to handle the antics of her ex-husband Andrew, who's threatening her campaign. Aide Quinn (whose affleable image hides his ruthless nature) presses Selina who snaps "take care of it," meaning to pay Andrew off. Instead, Quinn assumes he's been given a murder order and arranges for Andrew to be killed in a boat explosion. Selina is rocked to realize she accidentally ordered her ex-husband's death.