Two interesting things from psychological research:

First, self-control is a limited resource. Studies have shown that self-control or self-regulation works like a muscle, and that if you use it for one task, you will have less of it on a subsequent task that requires self-control. Even if those two tasks are completely unrelated. For example, in one study research participants had to sit in a room with both radishes and chocolate on a table. One condition was allowed to eat the chocolate, the other condition was only allowed to eat the radishes. After this, people in both conditions had to work on an unsolvable puzzle task (obviously the research participants do not know it's unsolvable. It's a common way to measure perseverence or motivation). People who had to use self-control to eat the radishes and not the chocolate quit the puzzle task sooner than people who could eat the chocolate. Similar effects has been replicated in different ways with different tasks. Making choices or exerting self-control will result in decreased performance and perseverence in subsequent tasks, because of "ego depletion". (Positive emotions are one way to fix your ego depletion faster, or so I've read.)

Second, multiple studies have shown that self-discipline can be trained, making you less vulnerable to ego-depletion. For example, in a study where people started working out regularly, they also started drinking and smoking less, eating healthier, etc. Another example, people who were taught money management also showed more self-discipline in other areas of their life (diet, exercise, less drinking and smoking, etc.). So apparently our capacity for self-control can be trained. By using self-control, you will get more of it, in ALL areas of your life.

http://psycnet.apa.org/journals/psp/74/5/1252/
http://onlinelibrary.wiley.com/doi/10.11...x/abstract