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->''The only thing that sustains one through life is the consciousness of the immense inferiority of everybody else, and this is a feeling that I have always cultivated.''
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 EmptyShell, 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 Only Sane Woman.
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 Only Sane Man 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 as the Only Sane Man 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 Only Sane Man 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. The comedy version will often end up being either a ButtMonkey or a ChewToy. 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]]. See also CassandraTruth, SurroundedByIdiots, and SurroundedBySmartPeople; contrast with the UnfazedEveryman. May temporarily overlap with WhatTheHellHero.
If several characters take turns being the Only Sane Man, they're playing with a SanityBall. If it's a two-person show, with one person playing the Only Sane Man 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.