Why Trust People

Why do we trust others? I mean when you start to actually think someone is nice and descent they turn around and act like total bitches toward you. So how do you know who's real and who's fake?? I get tired of listening to others I think I can trust talk about me behind my back. So the only thing I can do is watch what I say. Watch my back because chicks can get caddy. You never know when they will backstabbing you. Because there are ones out there who will turn on you very quickly when they don't get their way. Ever had that happen to you??