Why do people create fake profiles on online game sites ie. pogo & king .com's?

i enjoy online gaming. i particularly like pogo.com. but i cannot, for the life of me, understand why some people feel the need to create fake profiles and befriend then betray other people! i know it sounds sad and pathetic, but i've seen a lot of people get into relationships (as friends or more) and then get hurt when one of the two turn out to be "fake" and not at all what they made themselves to be. I'll admit, i befriended someone (TOTALLY platonic) just to find out that that person didn't really exist! why do people do this?!