Power Rangers: Especially in its first few seasons, the Rangers themselves were goody goods. Little to no negative behavior and all. But on occasion, Rita, Zedd or The Machine Empire would place a spell on the team or some members to cause problems (Such as Tommy debuting as an evil Power Ranger). Happened a good number of times. You'd Expect: That someone would attribute the odd behavior to a magic spell. Instead: The Rangers are dumbfounded by one of their own acting strange.
Mighty Morphin' Power Rangers, "The Green Candle": Rita has a candle that, when completely burnt out, will return the Green Ranger powers to her permanently. When Goldar captures Tommy, his presence causes it to burn faster. The Rangers set up a plan for Jason to hop through the portal. During the fight, a monster shows up and Tommy, not wanting to sit around, heads out in Dragonzord to confront it, but is quickly overpowered. You'd Expect: Jason needs a little more time - Either have Zack, Billy and Trini aid Tommy and form the Dragonzord Battle Mode or have the rest of the rangers form the Megazord without Jason, or thirdly, send another Ranger in to speed things up and get the candle out. Instead: Zack goes in and forces Jason into a Friend or Idol Decision which haunts the guy for years to come.
Another from Mighty Morphin, "Mighty Morphin Mutants": The monster, Commander Crayfish, and evil clones of the Green, Blue, and Black Rangers have undergone Make My Monster Grow and are fighting the Megazords. The Evil Rangers form a human chair and elevate Crayfish onto their shoulders, leading Billy to announce he's above their Blasters' range, leaving them sitting ducks. You'd Expect: Someone in this collective braintrust would think to disassemble the Megazord and let Kimberly take the Pterodactyl (which can fly) and use her individual blasters to knock Crayfish back down to the ground. And then finish him off with the Dragonzord Battle Mode. Instead: They keep barreling straight ahead, taking a few intense hits, then summon Titanus to simply overpower him (which worked, but still.)
Power Rangers Zeo and possibly other seasons, "Mean Screen": This week's titular monster is actually winning against the Rangers. You'd Expect: That the Machine Empire would realize that the Rangers only have one weapon they haven't tried: the Zords. However, part of the Ranger code involves not bringing them in unless the monster is itself giant. With that in mind, by remaining at normal size, the monster can wipe out the Rangers in seconds. Instead: Klank and Orbus are sent in to Make Their Monster Grow, which leads to it being defeated by the Megazord like all the others.
Another from Zeo, the energy draining monster Main Drain feigns a surrender despite the fact that he was WINNING against the Zeo Megazord and even their powerful sword slashes were just doing Scratch Damage. You'd Expect: That the Rangers would instantly know something was up and that he could drain their power at any moment, realize it was a trap and take the opportunity to use the finishing strike on Main Drain, even though it probably wouldn't have finished him off based on the fact that it took TWO finishing blast barrages from the Red Battlezord to bring him down, it would have briefly stunned the monster, giving them time to escape before he could finish them off so they could go back, regroup, and find a way to win. Instead: The Rangers buy into the fake surrender, with only Kat realizing too late that it was a trap. By that time, Main Drain had burrowed a cable into the ground and drained all the Zeo Megazord's power, even breaking their sword in two (to that point a Megazord had never had its weapon broken), and it ended up draining the command center's energy in the process. If not for Alpha teleporting them out just in the nick of time, King Mondo would have won right then and there.
In Turbo, the final battle is this trope personified. Goldgoyle, a monster that defeated both Megazords, was sent only to distract them so Divatox could launch an all out attack on Angel Grove. You'd Expect: A quick and hasty retreat once they realized they were getting their asses royally kicked, as the monster showed no indications of attacking Angel Grove or the power chamber. They'd ward off the attack by the Piranatrons while figuring out Goldgoyle's weakness, go back, and take care of business. Instead: They respond by self-destructing the Rescue Megazord, using a special superpowered version of the Turbo Megazord spinout (which does not finish off the monster), then suffer damage to where the Turbo Megazord is inoperable, losing both Megazords while giving Divatox time to attack. The events that were leading to the best season of all time, In Space, but still....
On that note, in an earlier episode, General Havoc's special zord, the Metallosaurus. You'd expect: The Turbo Megazord to jump out of the way of the sword-breaking tail slash and use the second, very powerful finisher used on Goldgoyle where it doesn't just spinout slash but launches itself through the monster, which would have undoubtedly defeated Metallosaurus with no problem. Instead: They let it break their sword and get their asses kicked.
In the final episode of Lightspeed RescueCarter Grayson has just thrown Queen Bansheera into the tomb that she had attempted to use to bring the Demons from the Shadow World into the real world. You'd expect: For Carter to close the lid on the tomb, thus ensuring that she will never return. Instead: He neglects to close the tomb, turns around to give a thumbs up to Ryan, and it leads to Bansheera grabbing him, pulling him into the tomb and attempt to pull a Taking You with Me. Thankfully: Diabolico arrives in the nick of time to save Carter.
Wes is forced into a 10-Minute Retirement by his Identical Grandson, Alex, who takes over his position as Red Ranger. Prior to this, Alex watched all of the rangers battles in his Mission Control, so he knows what their weapons and zords can do. When Frax unleashes his new robot, Dragontron, the team brings out their Shadow Force Megazord and its BFG. They get a clear shot, and... You'd Expect: Shoot him now! Shoot him! Instead: Alex has the team hold their fire. This allows Frax to warn his robot, thus ruining the shot and resulting in a battle in which Frax and the robot clear out. For extra points: He yells at the rangers and blames them for failing the mission when they just followed his orders to the letter.
In the next battle with Dragontron, the Time Force Megazord gets disabled by Frax's new Energy Siphon. To remedy this, the Rangers go after Frax and the Siphon. After clearing out Frax's Cyclobots, they corner the robot villain. You'd Expect: Alex would have a few Rangers pin down Frax while the rest disable the Siphon. Instead: Alex orders the Rangers to disregard Frax and go after the Siphon. While the Rangers question the logistics of this decision, Frax gets up and uses the Siphon on them. Left defenseless, the Rangers are saved by an unmorphed Wes, who takes out the Siphon by himself.
Power Rangers S.P.D. "Recognition", in a plot recycled wholesale from Tokusou Sentai Dekaranger: The Rangers have seized an alien criminal who wiped out ninety planets off-screen and additionally can swap bodies with others - but can't speak English (or Japanese in Dekaranger) without a translation device. The commander wants him brought in for questioning. You'd Expect: When escorting a potentially dangerous criminal, multiple Rangers should be escorting the guy to his cell, just in case. Instead: The Blue Ranger does it alone and falls victim to the alien's body swapping, and when the alien destroys the translator, he is left in no position to stop him. The alien, in the Blue Ranger's body, takes control of the Delta Base and even authorizes the Ranger's execution. Additionally: Especially stupid in SPD, as the Rangers regularly capture alien criminals in cards, and there's no real reason not to use them to transport the prisoner here. Dekaranger doesn't have this problem as they don't have capture cards; they're usually authorized to use lethal force instead.
Power Rangers Jungle Fury has the Rangers trapped in a TV game show. Unfortunately, the show is being run by the bad guys who are saying Screw the Rules, I Make Them!, with half the Rangers being eliminated from the game for petty rules violations (and of course, if they lose, the villains will have free reign to eliminate mankind). The host offers the Rangers the chance to give up some of their winnings for a trip to Hawaii. You'd Expect: The Rangers remember that not only are cash prizes at stake, but also the fate of the human race, so they shut up and keep playing. Instead: Lily jumps at the chance, claiming she's always wanted to go to Hawaii. For that, she not only loses some cash from the pot, but she's thrown out of the game as well.