Extroverts tend to put their own interests above the common good, but only if they are sure that they will not be judged by others.
In a cooperative game, volunteers could decide how many chips to keep for themselves and how many to put in a common pot. In the final, chips from the bank were distributed among all players. If each player picked a pot, everyone was in the black. But if others didn’t follow his example, he was in the red. When the players didn’t see each other’s moves, the extroverts tended to take the chips for themselves. But when the game was open, extroverts were even more generous than introverts. Perhaps in this case, the risk of judgment was a more significant factor than the joy of winning.
Philosophical Transactions of the Royal Society, 2015, vol. 370, № 1683.