Reading this and other short articles on this site, all documenting experiments in human psychology. Some of these have counter-intuitive results (or at least counter-popular-wisdom) regarding how external situations and other people's expectations influence our behavior, no matter how much we think it's internally driven or a matter of inherent 'character'. All of this is reinforcing ideas I'm working with in fiction... which is why I was Googling for it in the first place, natch! Check the links at the end of the page for the other articles if you're interested.
http://www.spring.org.uk/2009/12/when-situations-not-personality-dictate-our-behaviour.php