Supposedness. Who says characters have to act in a certain way? Keeping readers guessing is also what keeps them entertained and coming back for more. The best part of writing a character is watching them evolve. And not just the main character either, but all of them. Changing up the normal, the way their “supposed” to act, is not only fun, but interesting for author and reader alike.
Don’t get me wrong though. While you can evolve and entice it is still necessary to keep the important base characteristics that make your character, well, your character. So be careful of that fine line between evolving and an unrealistic 180. Unless of course there’s some serious plot reasons for it.