->''"The next time you get the urge to take over someone else's holiday, I'd listen to '''''her'''''. She's the only one who makes any sense in this insane asylum!"''
-->-- '''SantaClaus''', ''WesternAnimation/TheNightmareBeforeChristmas''
When there is a group of characters who are all just totally weird, either in general or in a particular scenario, the Only Sane Man is the only one who, well, isn't.
Picture this: Alice is a PsychoForHire, Bob is a CloudCuckoolander, Doug is an Empty Shell, and Emily is a MadScientist. Looks like your standard DysfunctionJunction. But then you have Gardenia. Gardenia is actually a very well-adjusted individual. She reacts with appropriate horror to things like Alice's finger collection and the crimes against nature that Emily calls pets. Gardenia is the OnlySaneWoman.
The other variant is where the other characters aren't ''always'' that weird, but everyone save one character is acting weird in a particular situation. For example, they might regard something absurd as SeriousBusiness, with the OnlySaneMan the only one who notices how crazy that is.
This latter variant also includes a standard comedy piece: something absolutely insane [[NoMereWindmill is going on]], but only one person notices (or cares). There are usually three stages, with a rough correspondence to the FiveStagesOfGrief: Bewilderment (Shock and Anger), trying to get others to see or admit the weirdness (Bargaining and Denial), and [[DeadpanSnarker bitter sarcasm]] (Acceptance).
In the more extreme cases, the poor soul may be trapped in a WorldGoneMad and/or wind up GivingUpOnLogic in frustration. Sometimes, though, they are NotSoAboveItAll. A character may also ''think'' of themselves at the OnlySaneMan without proper justification.
A TooDumbToFool character may be the Only Sane Man, although he is likely to be less worked up about the failures of others to see than in most cases.
The OnlySaneMan is [[TheReliableOne often relied upon]] as the OnlySaneEmployee. This character often ends up a KnightInSourArmor. For a more horrific version, see ThroughTheEyesOfMadness. For the sci-fi version, the IgnoredExpert is your go-to guy. If all the other characters are otherwise sane, and really should see something, but only one guy does, he's an EinsteinSue. The NietzscheWannabe is a [[EvilCounterpart villain who views himself this way]]. Occasionally, when the OnlySaneMan expresses his creator's opinions, he serves as an AuthorAvatar. See also CassandraTruth, SurroundedByIdiots, and SurroundedBySmartPeople; contrast with the UnfazedEveryman. May temporarily overlap with WhatTheHellHero.
If several characters take turns being the OnlySaneMan, they're playing with a SanityBall. If it's a two-person show, with one person playing the OnlySaneMan to the other's wackiness, it's a StraightManAndWiseGuy scenario. This trope is one third of a ComicTrio and part of the FourManBand.
TheWonka may well feel like this (or be this!) in a world that doesn't follow his thinking. Insanity is, after all, in the eye of the beholder, and TheWonka often has quite valid points.
'''NoRealLifeExamplesPlease You are not the only one that doesn't belong in an asylum, contrary to what you might think.'''