One of the studies I talk about in the book concerns a study done by Stanford psychologists. They had two groups of people. One group they had memorize a two-digit number. The other group they had memorize a seven-digit number. Then they marched these two groups down the hall and gave them a choice between two snacks.
One snack was a rich, gooey slice of chocolate cake. The other snack was a responsible fruit salad. The people who memorized a two-digit number were twice as likely to choose the fruit salad as the people who memorized the seven-digit number, who were twice as likely to choose the chocolate cake. And the reason is that those extra five digits — doesn't seem like very much information at all, just five extra numbers — so overwhelmed the prefrontal cortex that there wasn't enough processing power left over to exert self-control.
So that gives us a sense of just how limited in capacity our brain actually is and, I think, points to the fact that we should absolutely be aware of these limitations.