This is when the clinically insane person turns out to be The Only One who has the right stuff to stop the catastrophe or Big Bad. It could be his bent perceptions allow him to see things "normal" people can't. Or maybe the bad thing that happened was so completely out of the realm of possibility that only the total nut job prepared for it. Keep in mind, what separates this from Sociopathic Hero or other crazies is that this character's madness is essential to the task. If he was not crazy, he could not do it.
This guy put the Crazy in front of Prepared and Awesome, but don't confuse him with an Ignored Expert or The Worm Guy, who are not actually insane, just misunderstood. Not to be mistaken for his padded-cellmate the Sociopathic Hero, who is a hero in spite of his anti-social tendencies, not because of them.
When the whole human race is composed of Heroic Madmen, it's Humanity Is Insane. Compare Crazy Sane, The Cuckoolander Was Right and Power Born of Madness, although this trope doesn't necessarily involve superpowers. See also Blessed with Suck and Disability Superpower.
- Crazyman from Continuity Comics, whose power is being crazy. "Crazyman" is recruited by a secret service as the "Plan B" to dangerous "unwinnable" situations. Danny is to the secret service as Monk is to the San Francisco Police Department, and comes up with solutions no sane man would come up with. If James Bond were insane, he'd be Crazyman.
- A The Sandman story has Delirium in a foul mood, having hidden herself away in her realm and cut off all access. In order to get to her, Dream recruits several mentally ill people, as only their flexible interpretations of reality would allow them to navigate Delirium's home unscathed.
- Common joke among Mathematics or Computer Science students and professors involves asking how many people became insane while studying in their departments. The correct answer is zero: insanity is a prerequisite.
- Redwall: In High Rhulain, the hare Major Cuthbert went insane after his daughter was killed by vermin. He ended up killing a sea monster single handedly.
- In Larry Niven's Madness Has Its Place, Jack Strather's megalomania and paranoid schizophrenia make him one of the few men left on Earth with the cojones to actually resist the invading Kzinti.
- The main character's severe autism means he's the only one able to objectively synthesize all of the information and determine just what the deal is with the Starfish Aliens they discover. Of course he's also unable to bond with other people or empathize with them, so...downer.
- The predatory instincts and complete sociopath nature of the ship's captain (who is an actual vampire) also turns out to be vital in second-guessing the otherwise indecipherable behavior of the alien vessel and its inhabitants.
- In C.S. Friedman's This Alien Shore, the Guerans (a mutant race descended from humanity) are all insane, which makes them the only ones who can pilot ships through hyperspace. In addition, the heroine's multiple personality disorder grants her a secret power that could alter the balance of power throughout known space.
- Jack Vance's short story "The Men Return" featured a world where causality had basically gone out the window. One character was barely surviving, trying to find patterns where there were none. The ones who were crazy before The Event on the other hand were basically gods.
- The eponymous Strange of Jonathan Strange & Mr Norrell must drink a bottle of distilled madness (causing him to lose his mind) in order to be able to see and interact with The Fair Folk on their own terms.
- Never Let Me Sleep: Whether it�s the way her brain naturally works, or the medication she takes for her disorders, Melissa is the only person not effected by the death sleep within the "South Dakota Quarantine Zone".
- 7Days: The only person able to pilot the Chronosphere is Frank Parker, inmate at a military insane asylum.
- There's a rule concerning "Insane Insight" in Call of Cthulhu that allows a PC going mad to obtain some hint from the GM as to what they're dealing with or the true natures of the cosmos.
- Dead Space: Isaac Clarke has the blueprints of the Marker in his head. This makes him the perfect guy to go about killing the source(s) of the Necromorphs, and allows him to read and decipher Marker texts. It also makes him paranoid, schizophrenic, and he often hallucinates dead people talking to him. Which is pretty par for the course for anyone who's survived close contact with a Marker, to be fair.
- Portal: Schizophrenic Doug Rattman was completely right in suspecting the operating system was out to kill everyone and so was the only survivor of the lab incident.
- The Secret World: Daimon is a firm believer in this, hence his astonishingly eccentric behaviour. As he explains in both dialogue options and cutscenes, he believes that only individuals who are utterly without structure, dignity and sanity can truly succeed in the dark days, and to this end has made himself as loose, adaptable and eccentric as possible. He even compares this to incidents where drunk-drivers somehow manage to survive accidents that would have killed sober motorists, reasoning that their survival is due to having lost all the self-respect that might have made them brittle, instead being malleable enough to walk away unharmed.
- Anghel Higure of Hatoful Boyfriend is trapped in a delusion that his life is some high-fantasy epic story and those around him are characters in the same. His fantasy stories are, in fact, a perfect metaphor for some of the other characters' personal storylines, including some very dark secrets about them that not even they know, the "spores" he rambles about are probably the biological superweapon samples the doctor has in the clinic, and his senses are highly sharpened by the paranoia of believing himself a fantastical antihero, enabling him to detect threats sooner even if he can't always communicate them.