Compulsive behaviour

I find that sometimes it is just hard to stop. If it is easy to do something and you have already done it in the past, why not do it again? Even when you know it is not what you are supposed to be doing. Like eating fries, making out with a jerk, watching a bad movie you secretly like, reading gossip online even when your mother taught you that people reading gossip are bad, wasting your time on FB, seeing the world in black and white etc.. Why is it so easy to judge other people but very hard to change our own behavioural patterns?