$($Dixit and Skeath p$\mathrm{.}117)(3$p$)$ An old lady is looking for help crossing the street. Only one person is needed to help her; more are okay but no better than one. You and I are the two people in the vicinity who can help; we have to choose simultaneously whether to do so$.$ Each of us will gain $($get pleasure$)3$utiles$$ from her success, no matter who helps her. But each one who goes to help will bear a cost of $1$ utile, this being the utility of our time taken up in helping. With no cost incurred and no pleasure derived our payoff is $0.$