Do NOT take the following seriously.

Suppose you are a sitting Supreme Court Justice. To some degree you are concerned about who your successor will be. As the political scientists put it, your ideal point is, well, you.  You want your successor to be as much like you as possible (if you're a conservative, just as conservative -- but no more conservative -- than you are, if you're a liberal, just as liberal -- but no more liberal -- than you are.) [I ignore the possibility that your actual behavior is itself strategic -- that is, you would like to be more liberal or conservative, but the conditions of the current Court are such that you are constrained to be no more liberal or conservative than your votes indicate.]

Consider the calculations you do today. Right now, your successor will take his or her seat as a result of a process in which a Democratic President is constrained by a Republican Senate. If you wait, there are four possibilities: another Democratic President similarly constrained, another Democratic President with a Democratic Senate, a Republican President with a Republican Senate, and a Republican President constrained by a Democratic Senate. You have to place probabilities on each of those possibilities, and then figure out how close a successor chosen under each of those conditions would come to your ideal point.

Without going through all the details, I suggest that, placing reasonable probabilities on each of the possibilities, it wouldn't be irrational for either Justice Ginsburg or Justice Scalia to conclude that retiring now would yield a successor closer to her or his ideal point than waiting.

But, of course, I'm asking you to suppose that you are sitting Supreme Court Justice. Which means that you have a quite high (probably irrationally high) sense of the contribution to the public good that you, and only you, can make. (Put more formally, you think that any successor will be so far from your ideal point -- again, you -- that small differences can be ignored.)

Mark Twain comes to mind: "Suppose you were an idiot, and suppose you were a member of Congress. But I repeat myself."