 That’s the basic idea at the core of decision theory, but it’s still a long way from being satisfactory. For one thing, this calculation assumes money is everything, which it surely isn’t. Suppose you need exactly $29 to get a bus home for the night, and all you have is the $10 bill in your pocket, which on its own is no use (even the cheapest drink at the casino bar is $11). So losing your $10 isn’t really much worse than keeping it—you might as well be broke either way. But gaining $19, now that’s worth a lot to you. If you can just get the bus back home, you won’t have to sleep rough for the night.