As he mentions, most people would see the preposterousness of testing a child’s potential based solely on the fact of whether he eats a marshmallow or not. Rather, I think most people see it as a predictor of a character trait. The character trait, the ability to delay gratification, is more likely to show up in children that can resist the marshmallow rather than the children that cannot.
It is this ability that is hypothesized to be able to bring higher degrees of success. It is easy to see how this can apply- we don’t party now in order to study and get better grades, we don’t eat that cookie in order to keep our weight down. We sacrifice something short term, that although it would bring us pleasure, would not bring us as much happiness and joy as achieving our real desires.
The draw of this theory is that this character trait, the ability to delay gratification, is something we can control. We can’t control our looks and our height. We can’t control (or at least, supposedly) can’t control our intelligence and IQ. We can’t control the economy. In fact, the amount of factors out of our control is higher than the things we can control. But this, this almost universal indicator of success, we can control.
We can set up our life to focus on long-term success rather than short term pleasure. We can focus our life on what’s important to us, and cut out the fluff.
I believe in “character is destiny” because I believe I can control the path I go on.