It has taken me almost my whole life to realize this. I try to surround myself with people who are much like me. I used to take what people said at face value, then I was stabbed in the back because I trusted them to easily. My words twisted and used against me.
I have noticed that a lot of people like to say what you want to hear, rather than tell the truth about something, as to not hurt your feelings. They would rather have you happy than angry with them. They aren't necessarily "bad" people with "bad" intentions...just people who think they are doing right by you.
People come and go in life. Even if they are causing a negative balance, you can learn something from them.