In my experience, roughly half of the people you will know in your lifetime will be lying, backstabbing pieces of shit. You may never find out about it, or you may find out, but keep it to yourself and let them think you're oblivious, or they may never betray you at all, only betraying the other people in their lives. They're pieces of shit, regardless.
The majority of the people in this world are scum, watch them carefully. Eventually, you'll find a handful of people you can trust.