Why do people lie?

I'm at the point where I don't feel that I can expect a truthful answer to the simplest questions anymore. Everyone lies all the time. For what? It's a waste of time for everyone. I don't think that I lie. Am I wrong? Do all these fucking liars go around thinking they're as honest as I think I am? I don't feel like I know anything for sure anymore. And I certainly can't trust a single human being on this earth. And I don't understand why it has to be that way. Because if I trust anyone ever again then I'm just lying to myself.