Most people do, don't beat yourself up over it. The whole concept of discipline and self control seems rather dubious to me.

Some things are easiest to deal with by changing your environment, eat too much junk food then don't keep any in the house, watch too much TV then get rid of the TV, spend too much time on the internet then cancel the broadband connection. I ride my bike everywhere because I don't have a car.

Other things you can trick yourself into doing, if you buy too many sweets when shopping then don't shop when you are hungry and always take a list. If you don't exercise enough then book a regular session with a trainer where the cost of cancelling is high.

Big changes in your life are also a good time to change other things, moving house, getting a new job, getting married are all good times to instigate a new regime.