Sometimes "best guess" is the contract. Obviously many applications can't tolerate that, but surprisingly many can. The user just needs to know what the trade-

Sometimes "best guess" is the contract. Obviously many applications can't tolerate that, but surprisingly many can. The user just needs to know what the trade-off is. And "best guess" can be hard to characterize, so you need to be extremely careful. But sometimes it's a big win for a low price.