Why can't we keep the promises made to ourself?

Why do we repeatedly fail to go to the gym? Why do we fail again and again in our attempts to eat right?

I think that doing things right over a period of time consistently is an habit, so like all habits, these have to be done repeatedly over a point of time, remember that this is the most difficult and crucial time for you success, once we get past this stage, things grow on us, and secondly just turning up is better than not turning up at all, to elaborate this, everyone of us, have these days where we had too much to do the previous day and we just don't want to go to the gym, or feel like working out, but it is very important for us to just turn up at the gym, or the jogging track, ready for the workout, maybe the exercise for that day may be toned down but it is important not to skip and be regular, so that it becomes an habit, and thirdly, mentally keeping yourself motivated is very important if you have to lose weight, you got to keep imagining yourself thinner, leaner, and always have a mental picture of how you want to look in your mind so you stay focused for longer periods of time, use that motivation to drive you to a leaner and fitter you and fourthly use the positive responses from people, like "Matt, you look thinner today?" to push yourself further, convert all the positive vibe into positive energy, and then use the positive energy to work harder. Fifthly, believe in yourself, to achieve what you have set out to do, think of what fun you can have if you looked like you wanted, always prioritise yourself as important. Never give up. Failure is the stepping stone for success, the more you fail the more the chances of you making it. NEVER EVER GIVE UP.