Jack and Jill, who are partners in parenting, have sex sometimes, and are not convinced of the sanctity of monogamy. Jill wants sex more often; Jack doesn't. Jack suggests that Jill can seek out other people to have sex with if she wants more. Just like Jill often plays chess with others. Jack thinks this stance is sufficient and that should be the end of the issue.

But Jack is wrong. What he has missed is that Jill doesn't want more sex *with anyone*, she wants more sex with him. Whether this desire of Jill's is rational, is an open question I won't go into. But suffice it to say that Jill does have this preference. And the solution almost undoubtedly is not for Jill to want less sex to the level Jack currently wants. Rather it is probably more like: Jack will want a little more because he cares about Jill; Jill will want a little less because she cares about Jack; maybe or maybe not Jill will get some sex elsewhere; and Jack and Jill will looks for ways to make sex more interesting/enjoyable for Jack.

In theory, this can apply to chess too. But caring about who one plays chess with is not very common in our society. With sex, it is common to care about that.