Willpower and the problem of the lack thereof are pretty hazily defined here. Poor personal performance is a complicated issue that "Get sleep and exercise" is a poor prescription to. Poor organization, personality conflicts, attitude issues, perfectionism, and poor self image will make even the most well-rested and healthy person underperform at work.

I highly recommend "Procrastination: Why You Do It, What To Do About It" by Jane B. Burka and Lenora M. Yuen and "Getting Things Done" by David Allen for a deeper examination of these issues and some solutions.