Existence of ego depletion very doubtful
A popular concept in modern psychology is ego depletion (see Baumeister & Tierney, 2012). Briefly put, the ego depletion model says that self-control or willpower depends on a limited amount of mental energy. When you try to concentrate or control yourself for a long time, according to Baumeister, you use this energy and you will slowly but surely run out of it. The more this resource gets depleted the harder it gets to keep controlling yourself. This ego depletion effect is supposed to be general. Each task which requires self-control depletes your resources and when this happens its gets harder to control yourself for whatever task or seduction. According to Baumeister, you then need to supplement your resources, for example by eating or sleeping.
Previous research: ego depletion model is too simple
As I wrote before (here) there are two lines of research which have demonstrated that the ego depletion model is too simple. First, Moller, et al. (2006) have shown that ego depletion does not happen for all activities. According to these researchers, it does happen for activities for which the person has a controlled motivation and it does not happen for activities for which the person has an autonomous motivation. Second, Job, et al. (2015) have demonstrated that mindset is relevant. According to these researchers ego depletion does happen for people who believe that willpower is a limited resource but not for people who believe that willpower is an abundant resources and a skill which can be developed.
New study: ego depletion may not exist at all
Carter. et al. (2015) did multiple meta-analyses to analyse previous findings about ego depletion. They did three things different than previous researchers: (1) they used data from both published and unpublished studies, (2) they used improved inclusion criteria, and (3) they used cutting-edge statistical techniques. based on their analyses, they conclude that there is very little evidence for the existence of ego depletion. For more details, read this document.