Thought this might be an interesting read for us, heh:
"A thousand positive remarks can slip by unnoticed, but one "you suck" can linger in your head for days. One hypothesis as to why this and the backfire effect happens is that you spend much more time considering information you disagree with than you do information you accept. Information which lines up with what you already believe passes through the mind like a vapor, but when you come across something which threatens your beliefs, something which conflicts with your preconceived notions of how the world works, you seize up and take notice. Some psychologists speculate there is an evolutionary explanation. Your ancestors paid more attention and spent more time thinking about negative stimuli than positive because bad things required a response. Those who failed to address negative stimuli failed to keep breathing."
Full article is here: http://youarenotsosmart.com/2011/06/10/the-backfire-effect/