I think some are excellent intuitives (something anyone can develop-intuition), have general empathy, logical guessers and great wanna-be psychologists and therefore think they're psychics because they can guess a couple of details here and there and make mini-predictions. Fun fact: anyone can speak to their closest girlfriends (if they have decent ones to began with that aren't apathetic) and tell them their situation and I can bet you that those girls can make the same exact predictions and throw in some timeframes here and there. I also made predictions for myself and have gotten them right whereas those psychics have gotten them wrong. Am I psychic? Nope, just intuitive coupled with empathy and I am good at weeding out people's thought processes and intents due to my own life experiences.
I think the real psychics are the ones who can state extreme specifics and end up being right. Extreme specifics that there is absolutely no way of them knowing. For example, a birthmark or when you and that person started dating vs when you guys ended things. Or if they can pull out actual names and dates. I know a psychic on CP.com who is well known for this and it is because she is a channeler. I think she is the real deal.
I also think there are some who believe they genuinely speak with angels, spirit guides, etc., when in reality it is just in their head. Ouch, I know, but these things DO happen.