and sometimes involves choosing right,

有时选右的情况
it must be the case that what?

那么这一定满足什么条件呢
It must be the case that both left itself and right itself

这也就是说选左和选右这两种情况
are both themselves best response.

本身也一定是最佳对策
If she's mixing between them,

如果她混合了选左与选右
it must be that both choosing left or choosing right

那么选左和选右这两种策略
are themselves best responses.

本身也必须是最佳对策
If they weren't she should just drop them out of the mix,

如果不是她就会排除它们
that would raise her average payoff.

因为只有这样才能提高平均收益
Right, just like we dropped out the short T.A.'s

就像我们排除最矮的助教
to get a high height

来提高平均身高
and we dropped out the failing Yale students to get a high GPA.

我们排除了挂科的同学来提高GPA