Why are people on this site so mean?

I want to know why people come on here and answer questions like a jerk. I see lots of people asking sincere questions and in need of real advice (myself included) and the answers are nasty and thoughtless. Take a minute and consider the position of the person and if you can't offer some real advice - be it positive or constructive criticism, don't bother. And if you don't understand the question, don't bother either, instead of uming things.