Weight-loss programs are often very strenuous for the participants. Many people often go off track in their programs because there is too much temptation with watching everyone else eating food that they want. However, the biggest reason to fail at a weight-loss program is loss of motivation.
Motivational techniques such as competitions of "who can lose the most weight" or "who can go a week without eating cake", can really boost moral of the winner, and inspire the other competitors to do better.
It is in human nature to try and win against a challenge that is put in front of them.
