The psychological principle that best explains why we overeat in social situations is Social Facilitation.
Social facilitation is the propensity for the presence of others to increase a person's performance on a task.
One of the effects of social facilitation known as the co-action effect describes how your performance on a task improves just because there are other individuals doing the same task as you.
The three variables involved in social facilitation are:
Now, in a social setting such as parties and celebrations, you may be probably excited and engaged in eating much more just because other people are doing so.
Learn more about social facilitation here:
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