"I think I can, I think I can," said the Little Engine Who Could. And it worked. Positive self-talk can produce amazing results. The problem arises when there is a strong undercurrent of a negative self-concept that conflicts with the positive affirmation. Just tacking on a mantra or affirmation to a hardened, cynical attitude will produce mixed results at best. For an affirmation to work, it has to be received in you inner life. You have to be receptive to this new idea, or otherwise you will reject it, unconsciously or unknowingly. 

Like a farmer who tills the hard, dry soil to receive the seed, we also must clear the way and be open to plant new ideas. The best way is to take the advice of Emile Coue and repeat often: "Day by day, in every way, I am getting better and better."