When social norms support good behavior, we must be careful and leave them intact. In the IsraelI daycares, the mistake was instituting a fine, a punishment that eroded the existing social norm. Similarly, we must be careful whenever we introduce rewards for good behaviors people are already doing. When we do so, this can cause an overjustification effect, in which people become reliant on a reward for a behavior that they were already happy to do without any incentive.
