Relative to the maximum cooperative payoff, the actual equilibrium payoff can be arbitrarily small.
Please be careful to specify “Nash equilibrium” here, rather than just “equilibrium”. Nash is not the only possible result that can be obtained, especially if players have some ability to cooperate or to model their opponent in a way where Nash’s conditions don’t hold.
In actual tests (admittedly not very complete, usually done in psychology or economics classes), almost nobody ends up at the Nash equilibrium in this style game (positive-sum where altruism or trust can lead one to take risks).
Please be careful to specify “Nash equilibrium” here, rather than just “equilibrium”. Nash is not the only possible result that can be obtained, especially if players have some ability to cooperate or to model their opponent in a way where Nash’s conditions don’t hold.
In actual tests (admittedly not very complete, usually done in psychology or economics classes), almost nobody ends up at the Nash equilibrium in this style game (positive-sum where altruism or trust can lead one to take risks).