The main point of cognitive evaluation theory is that the introduction of external rewards will lead to the decrease of the overall motivation level. If we give an external reward to a person who is engaged in the work he is interested in, it will lead to his interest in the task itself decreasing.

It can be seen that the old man gave the child 25 cents in the hope that this external reward would reduce the child's interest in play itself. At the same time, reducing the amount of money per day obviously has an excessive effect, and the behavior of letting children play has changed in essence from the essence that play can bring happiness to the concept that play can get rewards. Finally, when there is no reward, children naturally give up the task of playing.

Among them, the daily reduction also reflects the elderly's understanding of reinforcement theory, which is quite impressive!