This is a snippet from an article in Psychology Today.

It may be true that we can do almost anything we set our mind to. But if our mind is our worst enemy, we simply may not be able to believe this otherwise inspiring (and motivating!) maxim. That is, whatever anxieties we may have about failing, as well as our poor sense of self-efficacy, may either keep us from starting a task or prevent us from completing it. And even if we do end up finishing it–because, say, it’s a job requirement and we absolutely must–our pattern of delay will still persist. Unresolved self-doubts (deeply programmed within us) aren’t automatically erased by an expedient action and will reaffirm themselves (through some sort of procrastination) the very next time we’re obliged to do something.

In my experience, people who lack self-discipline also lack fundamental self-esteem. And here the latter deficiency seems to feed directly into the former. That is, significant defects in our self-image undermine our confidence in our abilities, and this lack of self-confidence negatively affects the development of self-discipline–which of course is necessary to accomplish just those things that would enhance our self-esteem. Psychologically speaking, this has got to be one of the most vicious of vicious cycles