"Children were left in a room with toys, including a greatly desirable steam shovel, the #ForbiddenToy. One-half of the group of children were told that there would be severe punishment if they played with the forbidden toy and told the second half of the group that there would be a mild punishment for it. All of the children refrained from playing with it.
Later, when the children were told that they could freely play with any toy they wanted, the children in the mild-punishment group were less likely to play with the steam shovel. The degree of punishment was insufficiently strong to resolve their #CognitiveDissonance; the children had to convince themselves that playing with the forbidden toy was not worth the effort.
In a variant, without music in the background, the control group were told to avoid playing with a forbidden toy. After playing alone, the control-group children later devalued the importance of the forbidden toy. In the variable group, classical music played in the background while the children played alone. In the second group, the children did not later devalue the forbidden toy.
In an earlier experiment, the researchers indicated that the actions of #HandWashing might inhibit the cognitions that reduce cognitive dissonance.
https://en.wikipedia.org/wiki/Cognitive_dissonance