This can be one explanation of this experiment, but not the only one. I would look at it from a different perspective: One group of people felt good about themselves, and the second group did not. It this situation it was telling them that they have higher willpower, but it could be anything. Probably if you would tell them the first group “You are very intelligent”, the result would be the same. The group that felt good about themselves, they allowed themselves for a price. “You’re doing good, you deserved a cigarette!”. I believe there is nothing to do with relying on willpower, but with basic mechanism of rewarding ourselves.