Something interesting that they get into later is that people who have that type of self control are the same people who are able to control their conscious mind.
For example, people are shown four words, then shown a bunch of words quickly and told to press the button if the first or second are seen (but NOT the third and fourth). After doing that for awhile, they switch -- they have to press the button only if the third and fourth word are seen. People will self control do considerably better at this test, because they can control what's in their conscious mind better.
Another similar test was being shown a bunch of faces and having to press the button when they see a smiley face, then after awhile, told to press it when they see a frowny face. Again, it's about controlling what's in the working part of the brain.
Something that's interesting about this -- you can see from a very young age the people who have self control. The people who have self control will generally maintain it throughout their lifespan, and those who don't rarely pick it up. The people who maintain self control are the ones who are the most successful. Therefore, you can predict success from a young age, and you can therefore predict failure from a young age. So basically, we live in a world where success/failure can be predicted by the time you're 4 years old, based on factors that are completely out of your control. Sucks to be one of them!
The other question is, can self control be taught, especially to children?