Everything you do earn is cumulative. That doesn’t mean that industries stay good forever, or businesses stay good forever, but in learning to think about business models, what I learned at 20 is useful to me now. What I learned at 25 is useful to me now. It’s like physics. There are underlying principles, but now they’re doing all kinds of things with physics they weren’t doing 50 years ago.

But if you’ve got the principles, if you know what makes a good business, if you know what makes a good manager, if you know what makes a good product, and you learn that in one business, there is some transference to other businesses. As you go along, you learn what things you’re not going to understand. Knowing what to leave out is just as important as knowing what to focus on. Somebody said how to beat Bobby Fischer; you play him any game except chess. And so I don’t play Bobby Fischer at chess.