Bauermeister and Tierney discuss, in Willpower, the results of years of study on this subject. What they've discovered is that everyone has a certain amount of willpower, which the person then proceeds to use up during a day. If you use up lots of willpower trying to get through the day at a job that you hate, you will have less willpower at other times of the day.
One study followed college students at finals time. The college students (not surprisingly) wore dirty clothes, ate junk food, and neglected to bathe or clean their room. Instead, they either studied or wasted time procrastinating before studying. The exam preparation took all their willpower, and did not leave enough for them to maintain more reasonable standards of cleanliness.
Other studies dealt with decision fatigue. People forced to make many decisions(such as deciding what to add to their bridal registry) tended to finally break down in fatigue. They broke down even more so if they have nothing invested or lacked real control in the answer.
Finally, Bauermeister and Tierney looked at the effect of possiblity on willpower and decisions. I will discuss this more in the next post.