I was mostly thinking about mulligans. If you kept a one land hand and go on to win because you drew three lands in a row, that doesn't mean keeping it was the right decision. Conversely, if you do mulligan your 7 card hand and then end up with completely unplayable 6 card and 5 card hands, that doesn't mean that you should have kept your original hand.
Perfect example.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).