This does happen quite often, and the reason behind it is that they don't teach you these stuff at school; unless ofcourse, you have a keen interest in History or Politics. Eitherway, by bestowing your trust to someone you're knowingly and willingly puting yourself in a situation that might lead you to be taken advantage of. The easy way to avoid this is to trust NO ONE and distant yourself from the realm of naivety. Some people have the smarts to know this and others will learn the hardway, such as you. I could go on and say stuf like: trust would be meaningless without betrayal and blah blah, but you already know. If you try to understand it, you will eventually begin to enjoy it and appreciate it's beauty. The claws of causality are tighter than you might think.