Answer: situational strength or strong situation.
Step-by-step explanation:
Situational strength when one is affected by certain cues influenced by the particular environment to act in a particular way.
This strength gives someone a pressure to as they get involved in a particular behaviour or reject a particular behaviour.
This psychological pressure will cause someone behave that particular way irrespective of their personality.
In a strong situation situational strength is too high which means even if a person is an introvert or shy or not a people person however they will be influenced by the situation to act a particular way that may not be normal even to them.
During family gathering everyone get excited and they are in the mood that no one wants to be left out because it is a family gathering after all which means having fun together a s a family. Even those who can't do certain stuff like singing will always join together in family gathering this is because of the strong situation presented by the gathering of the family which increases the situational strength .