Resolutions don't work! Inspiration as a motivator is extremely unreliable: like sex or Chinese food, it just doesn't last. When we first make a resolution we get inspired and are filled with the neurochemistry of motivation. This inspiration is maintained by our ability to sustain mental pictures that stimulate us. Depending on the ability to conjure the results and be excited by them, to "picture" the results, this motivation can last anywhere from four days to three weeks. As our pictures of the intended result lose their charm, our motivation and its chemistry fade, and ultimately we can't reignite it. We go into failure and resignation, and worse, we add to a history of failure and it starts to affect our self-esteem.
We can't rely on an effort of will to create anything; we need to learn how to manage our own minds! Stop blaming yourself for failing and stop faulting your mind for what it cannot do. You have to learn how to use the mind successfully. The only way to sustain motivation is through creating easy habits of the mind that build on success.
First rule: make it really, really easy!
Instead of saying "I will lose forty pounds!", decide to lose one pound. Instead of saying "I will lose that one pound in one day!", decide to lose one pound in a week. You can achieve that, yes? You'll be tempted to say that this is too easy, but observe. If you lose one pound in one week effortlessly, you have succeeded at losing weight. You are now on your way to building a history of success and giving yourself positive reinforcement. Every little success feels like "winning". In addition, you are not limited to losing one pound, you are simply stating that one pound is your goal. Do more if you like, but only require that you do that one easy pound. By making it achievable you build a habit of accomplishment that will be so much more inspiring and sustaining than the dramatic declarations and failures of resolutions.