[kwurk] Show IPA
a peculiarity of action, behavior, or personality; mannerism:He is full of strange quirks.
People are quirky, so it makes sense that characters in novels should have their own set of quirks too. Quirks can make characters easier to relate to and are essential to setting characters apart from each other so the reader never gets confused about who is saying/doing what when the character's name isn't used.
That doesn't mean a character with a habit of winking should do so several times a scene though. Even if quirks are described sparingly, readers will pick up on them and those mannerisms will find their way into the reader's imagination of the scenes without the writer having to constantly specify them. And quirks shouldn't be shared between characters. If three characters have a habit of winking, they will start to blur and the reader may confuse them. In my own writing, I try to give each character a maximum of two to three unique quirks which I keep track of using character worksheets in Scrivener (just to make sure none overlap).
Writers can get carried away with quirks too. If giving a character a couple of quirks increases relatability, too many quirks quickly decreases it. Not many people can relate to a character who has enough quirks to make them sound more crazy than quirky. Then again, some stories are completely based on a particular character's quirks - ones which may be so strong that the character has a difficult time functioning in society. If that's the case, then any quirks in the other characters should be limited and should not be emphasized.
Here are some helpful blog posts on making effective use of quirks in writing:
What do you think? Have you read any novels/watched any TV shows or movies where overdone character quirks stole the show? How many quirks do your characters have and do you keep track of them?