Decision fatigue - http://www.nytimes.com/2011/08/21/magazine/do-you-suffer-from-decision-fatigue.html?_r=1&pagewanted=all

• You have a finite amount of energy to make decisions.  After you use it up, you will not have the willpower to carefully consider the choices to make a GOOD decision.  
• You will most likely choose the default option, the short term quick payoff option, or decide to eat Cinnabons after shopping all day.
• Ego depletion manifests itself not as one feeling but rather as a propensity to experience everything more intensely. When the brain’s regulatory powers weaken, frustrations seem more irritating than usual. Impulses to eat, drink, spend and say stupid things feel more powerful
• To restore your willpower you need to glucose for your brain.  A small shot of glucose will enable you to temporarily increase your will-power to make good decisions
• “Good decision making is not a trait of the person, in the sense that it’s always there,” Baumeister says. “It’s a state that fluctuates.” His studies show that people with the best self-control are the ones who structure their lives so as to conserve willpower. They don’t schedule endless back-to-back meetings. They avoid temptations like all-you-can-eat buffets, and they establish habits that eliminate the mental effort of making choices. Instead of deciding every morning whether or not to force themselves to exercise, they set up regular appointments to work out with a friend. Instead of counting on willpower to remain robust all day, they conserve it so that it’s available for emergencies and important decisions