The Clans from Battletech suffer from this when they invade the Inner Sphere. One of the biggest reasons for their failure is that the Inner Sphere refuses to fight to the Clans' rules, and actually takes advantage of the Clans' adherence to their code. Example: Clans traditionally begin battles with a challenge that states how many troops they are committing to the assault, and asks the enemy what they're preparing to defend with (this actually makes sense for inter-Clan warfare; they're short on resources, so they want to keep battles small so as to minimize casualties and collateral damage). The Inner Sphere, of course, would lie. Later averted by most Clanners, who simply come to the conclusion that anyone who doesn't want to fight by the rules shouldn't be protected by them.
Another reason for their failure lays in the fact that they must quantify their honor. For the Clans honor is not an abstract concept; they were created by a Proud Warrior Race Guy. When preparing for combat they will enter into bidding rounds and the lowest bidder will have the honor of proving that they bid exactly the right amount of troops needed to win the battle. Clans defy reason when their commanders will willingly bid lower than the minimum number of troops needed to win the combat, and that according to Clan estimates!
Prior to the introduction of the Clans, this was the hat of the Draconis Combine, which as a faction embrace a romanticized version of samurai honor. Probably the best example of it is this: if someone ordered a retreat, even if his unit was being overwhelmed by enemy forces and was in danger of being completely wiped out, he was expected to commit sepuku. Prior to the Clan invasion, the Draconis Combine's military took a very dim view of retreating from a fight regardless of the situation and placed a high expectation that you would try to fight individual duels with enemies instead of using group tactics. After the Clans invaded, the Combine was forced into adopting more pragmatic means of fighting since their traditional methods proved to be far less effective against the Clans' superior technology.
Warhammer 40,000: Space Marines generally eschew camouflage in favor of wearing distinctively-colored armor, and often have troops whose primary purpose is to bear banners conferring only psychological advantages.
This is more an aesthetic choice: Space Marines are in part analogues to knightly orders and warrior brotherhoods of old, and they're awesome enough warriors that camouflage isn't really a big deal. A better example would be times where a squad, company, or even entire Chapter of Space Marines go up against overwhelming odds to recover some sacred relic of their Chapter, which may very well be nothing more than a tattered old banner.
While it is an aesthetic choice, it is noted that the Ultramarines, whose codex tends to be the rules Space Marines go by, consider stealth and indirect warfare cowardly, which contributed badly to the Horus Heresy when their Primarch Roboute Guilliman refused to acknowledge his brother-primarch Alpharius for his brilliant and flexible combination of adaptive military combat and undermining the enemy from within, even when Alpharius went to extreme lengths to prove that his methods were worthy, because he judged Alpharius's deviation from the rigid outlines of the already established doctorines dishonorable. This would come back to bite Guilliman later when the Alpha Legion turned traitor, because Horus was one of the only primarchs who appreciated them, and underestimating their adaptable tactics cost the Ultramarines dearly in combat and allowed the Alpha Legion to continue to operate with impunity within the Imperium.
Ironically the current state of the Codex is that it has so many tips on how to be a Combat Pragmatist and generalized tips (like use of camouflage) that even following it to the letter allows a Marine to be very tactically flexible.
The Horus Heresy novel 'Know No Fear' shows us Guilliman's real problem with the Alpha Legion isn't so much that they were dishonorable, but that their thinking was inferior. Guilliman preferred strict structure and fighting enemy combatants, while Alpharius taught his Legion to favor unstructured combat and command; to attack from within, and to not limit their targeting to military targets. While in the 41st millennium Guilliman's attitude seems silly, it made a lot of sense in the 31st millennium - It had made the Ultramarines the uncontested, most successful Space Marine legion of the Crusade, taking more planets then any other. In addition, their straight, honorable combat often made integrating whoever the conquered into the Imperium far smoother and easier due to the respect of their defeated foes. The Alpha Legion tended to leave planets confused, decimated, and altogether very, very unhappy with them. It should be noted, however, that the Alpha Legion did not turn to Chaos over this minor spat - It's just why the current Ultramarines think they did. Which is more of a Pride Before Reason problem.
The obsession the Dark Angels have with hunting their turncoat members, the Fallen, ultimately falls into this. The sheer dedication the Dark Angels have to both wiping out all of their traitors and keeping their very existence secret from the Imperium in order to preserve their reputation as noble, honorable, loyal Space Marines means they will do things like abandon critical war objectives to chase after rumors of the Fallen, leave allies to be slaughtered, use their allies as bait or cannon fodder, and murder any Imperial who may have potentially discovered the secret. All of which is causing their reputation to be lost and making the Imperium regard them with just as much distrust and loathing as they fear the revelation of the Fallen's existence will bring. And any of their number who realise this and argue that they should stop this self-destructive spiral simply gets labelled as a Fallen.
Notably averted with the Tau, who stand out among the various races for actually doing pragmatic stuff like retreating when the situation turns dire (they consider last stands to be a desperate manouver and any commander who gets himself into such a position to be incompetent at best) and actually installing ejecting systems into their vehicles to save the pilots. The Imperial Guard wants to avert this, but the Commissar often "insist" they not.
Not that the Eldar are immune- One Avatar of Khaine (a giant living metal incarnation of their War God that requires the willing sacrifice of an Eldar warrior) was summoned to fight a Tyranid fleet. He stood on the battlefield issuing chalenges to the Swarmlord... who promptly directed half a dozen Carnifexes at the Avatar.
One race encountered prior to the Heresy had abandoned all-out warfare in favor of battles in specialized arenas. When the Imperium dropped by, they found the aliens armored up, weapons in hand... aligned neatly in the arenas and looking up at the ships in orbit waiting for the humans to land and fight them. They didn't last long.
The still-really-popular Marvel Superheroes RPG had this as a game mechanic. You couldn't use Mind Controlin any circumstance without losing Karma unless you were a villain. The idea being, of course, that the GM should always include a way to win without removing a person's free will. This was a superhero game, after all!
The godess Rondra and her church of the pen & paper RPG The Dark Eye are a fine example of this trope: Over the course of time Rondra degenerated from a goddess of war into a goddess of honor, going so far as to deem battles between armies and the art of war (strategy and tactics, that is) as "necessary evils" and only approving of one-on-one combats, which meet certain standards of honorable behavior. This development hasn't been without consequences in the game world itself: it has been mentioned that army officers tend to worship Hesinde (a godess of knowledge) or Phex (a trickster god of luck and wits) instead of Rondra. Not to mention Kor, a merciless god of bloodshed and mercenaries, who has a considerable amount of followers amongdisillusionedwarriors. And it seems as if yet another god is preparing to compete with Rondra and take over her old domain: Nandus, a god of reason, whose followers unsurprisingly prefer reason over honor.
High Compassion and Valor virtues in Exalted can create an ersatz form of this trope.
Additionally, the optional Merits and Flaws system gives "Code of Honor" as a Flaw; its value varies depending on how much it restricts your actions.
Virtues work this way in Scion. If a character wants to go against what their virtues would compel them to do they need to make a dice roll and fail to take the action, for example a character with Courage would have to fail a Courage roll to pass up on a fight with a dangerous opponent or willingly accept help from another person. If a Scion ignores their virtues too much they succumb to the virtue extremity and act out the extreme of the virtue.
The trope could be called "Virtue before Reason" in Scion's case, as even the ones that have almost nothing to do with honor (for example, Expression, which is all about creating art of all kinds) will still demand you follow them even when NOT following them is more prudent. This is even the case of the Dark Virtues that the Titans and their spawn use-for example, passing up an opportunity to torment a Scion or even attempting to invoke Why Don't You Just Shoot Him? requires a failed Malice roll. That's right-Titanspawn would rather engage in Bond Villain Stupidity instead of killing you right then and there. At least the game mechanics give a reason for it.
The Adamantine Arrow of Mage: The Awakening have the importance of honour enshrined in their creed as "Enlightenment is Honour". The Arrow believe that oaths are a deep expression of one's soul, and that fighting without honour is meaningless, so when they give their word they take it very seriously. That said, they are still encouraged to consider a situation carefully before committing themselves to anything, that their oaths should be simple and state exactly what they intend, as well as accounting for all possibilities (for example "I will be dead before you have this grimoire" is considered less preferable to "I will be dead before the enemy has this grimoire" since the former doesn't account for former enemies becoming allies). Overall, while they should keep to their word and their code, they should be careful not to cripple themselves with it.
One of the three Renown categories from Werewolf: The Apocalypse is honour, which is often associated with the law-keeper Philodox and 'just' deeds.
It becomes one of five Renown categories in Werewolf: The Forsaken, where it's associated with the Philodox-equivalents, the Elodoth.
A possible trait in GURPS is "Code of Honor". However, this is an unusual variant that has different degrees, including a Pirate's Code of Honor as a lower level than a Knightly one.
In Traveller there are several variations of this for different cultures. The Fteirle code of the Aslan is highly developed as befits a Proud Warrior Race.
Dwarves in Warhammer are this trope's posterboys. If they have some great dishonor that befalls them, sometimes as minor as not keeping a promise or a young dwarf being turned down by the girl they fancy, to something as major as kinslaying or failing to stop an assault on a stronghold, they lose the will to live. However, Dwarves physically and psychologically find it impossible to commit suicide, so they become Slayers and go fight the biggest baddest thing they can find until they find one that can kill them (they never fight to lose either). The paradox arises when Slayers become better and better at killing things (from trolls and giants to dragons and daemons) lose more and more honor.
This is a major problem in the Gotrek & Felix series; a Slayer's shame will not be relieved until death, but Gotrek seems to be completely unbeatable. Another is that the shame must be foremost on their mind when they die to relieve it, and Snorri, another slayer, has taken a lot of blows to the head over his career as a slayer and can't remember what it was.
The Dwarfs take it to an extreme with the Book of Grudges, where they recount every slight they've ever suffered, whether it be losing thousands of Dwarfs in battle to being slighted by two pennies for a construction project. The Dwarfs must avenge every single grudge they've ever suffered, and the grudges usually have some disproportionately high standards in which they must be fulfilled, i.e. the aforementioned act of being slighted by a couple of pennies means that the lord responsible be killed and his lands looted because they thought he'd done it deliberately. If they can't fulfill their grudges, well... there's a reason why there's a lot of Slayers.
The aforementioned grudges don't even need to apply to living things. In one battle inside a mountain pass, an Orc shaman who exploded caused a landslide that killed ten thousand Dwarf warriors. The Dwarfs' response was to declare a grudge on the mountain pass and proceeded to mine and demolish the entire mountain pass to pure rubble in retaliation.
It gets quite funny in the Total War: Warhammer video game, where this is a gameplay mechanic. One grudge requires you to send a saboteur to punish a rival Dwarf clan because they stole a halfling cook who made a special nutty fig pudding that High King Thorgrim Grudgebearer was fond of. Because nevermind that the End Times are upon us and Archaeon is rampaging through the Old World at the head of a colossal Chaos host and half of the continent is a burning hellscape, we simply cannot ignore the infamous "halfling pudding grudge".
Bretonnia is pretty big on this as well. Advanced weaponry that'd give them an advantage over Beastmen, such as guns and crossbows, are outright spurned (ranged weapons being only fit for commoners are acknowledged to be useful in combat, but they outlaw better weapons because it might give them ideas above their station). The Bretonnians get away with it through magicalPlot Armour and sheer balls.
Exploited by the Chaos character Wulfrik the Wanderer, who is able to issue inescapable challenges to enemy characters by insulting them. Battle needs your full attention? Screw that, a Viking two feet taller than you just called you a coward, let's go show him who's arrrrgh.
In Blood Bowl, the Bright Crusaders and the Heroes of Justice are the only teams who categorically refuse to cheat in any way. The problem is, naturally, they're the only people who have this compunction - in fact, for the Goblin team, cheating is their entire strategy. And naturally, for these teams, Failure Is the Only Option.
Vow of Honor is built around this trope. You play as discount paladins who gain and lose power depending on how well they uphold Fasaan's tenets. Depending on the GM's whims, staying honourable may be a minor inconvenience or hair-pullingly frustrating. (One way to violate the Righteousness vow is to be be emotionally affected by "times of tribulation.") To top it all off, the game is specifically designed to encourage philosophical conflicts between players.
Magic: The Gathering's Bant setting is so honor-bound that several knights wear backless suits of armor. This works due to the plane's color alighnment: White mana (law and order) dominates the plane, while Red (mindless destruction) and Black (corruption, selfishness) are absent. Sadly, it proves a bit less effective when those colors return.