Why is it hard to give trust?

Giving trust is actually too easy for me. And I have been cheated for several times. I determined not to trust anyone so easily and I'm still working on it. So I think it's not a big deal if you just feel difficult to trust someone. And that's the very thing I need to learn from you.

Trusting to someone is hard because if you trust him, he can hurt you. Usually I dont trust blindly to someone. In my case it usually goes like a tell him something little thing, I trust him that much, then he tells some little thing about him and so on. Later on I know so much about him that if he hurt me I surely can hurt him. Hurting doesn't necessarily means that other does it purpose. I have trusted someone and he broke my trust. He just wasn't person who I thought he was. He promise that he do somethinhg, but he was lazy and didn't do that. After that we still were friens, but every time when he promise something I just think that he just talks and he wont do it anyway.