You're the only person you have to live with the rest of your life
If you want to be healthy.. you have to BE HEALTHY. If you want to be rich, you have to do the work.. you have to find your niche, you have to take a chance. If you want a fabulous relationship.. you have to let go of the old ones. You can't change other people.. and you can't change your life without... CHANGING YOUR LIFE.
Those who are successful already tell themselves these things. They already believe it. I use the example, say someone hands you a puzzle, one of those brain teasing 3 dimensional puzzles, and says, "I think it has all the pieces". You may spend some time trying to put it together and if it gets too difficult you may say, "It must be missing some pieces.. this isn't working", but if they tell you that all the pieces are there you will be more willing to put in the extra effort because you know that it is solvable. Then there are others that will keep trying till it works regardless. If you are sure that you can do something you are more likely to accomplish your goal.