I’ve never thought about it, but my assumption has always been the two cards you’re offered are random, and the one you don’t pick is discarded. Which isn’t to say that the same card may not come up again later, but if it does, it was because it was generated at random, and not because it was one you discarded previously.
I have zero evidence that this is the case, just that it’s what I’ve always assumed, so when I pick a card, it’s solely based on which one is most beneficial at that moment.