"In life, whenever one tries to attain something, one encounters obstacles. Personal karma, habits and health problems get in the way. Just like when Moses went to the desert and heard voices that spoke of temptations, the mind devises tricks. If one makes a decision to fast and just read the scriptures for 30 days, the mind will play tricks during that time. The tendency of the mind and senses is to want only pleasure. The mind is so powerful, it will discern a little headache so that one can start to make excuses for not practicing. One might say, 'I'll start in the New Year' over and over. Then the New Year passes, and one is still over-indulging and generally carrying on as before. One feels that one cannot stop and change behavior, and delays the decision until their birthday. In a short time, it's the new millennium. So it goes as you continue to do the things you do not really choose to. One acts automatically due to past habits. Then one day, you are 80 years old and it is too late.
"It's best to make a contractual promise. Write and sign the document, then give the promise to someone in whom you believe to help insure that you stick to your word and follow through with right action."
-Dharma Yoga Life of a Yogi Teacher Training Manual