Willpower (2011) by Roy Baumeister and John Tierneyis a solid, reasonably entertaining combination of a popular science book and self-help book.
The book discusses a number of psychological experiments on willpower showing how blood glucose levels are closely related to the amount of willpower that you have. Being tired or hungry for good food causes people to have less willpower.
The book goes on from there to look at people who appear to have lots of self-discipline. It was hypothesized that these people would have more self-control in experiments but it turns out that they did not. What they were able to do was to form habits that lessened the need for self-discipline.
The book goes on further to state that parents need to instill the ability to use some will power with judgement to create good habits that mean that willpower isn’t depleted when doing required tasks.
The book is informative and insightful and well worth a read.