The ethical rule is from Samuel Johnson who believed that maintenance of easily removable ignorance by a responsible office holder was treacherous malfeasance in meeting moral obligation. The prudential rule is that underlying the old Warner & Swasey advertisement for machine tools: "The man who needs a new machine tool, and hasn't bought it, is already paying for it". The Warner & Swasey rule also applies, I believe, to thinking tools. If you don't have the right thinking tools, you, and the people you seek to help, are already suffering from your easily removable ignorance.

It's hard to predict what will happen with two brands in a market. Sometimes they will behave in a gentlemanly way, and sometimes they'll pound each other. I know of no way to predict whether they'll compete moderately or to the death. If you could figure it out, you could make a lot of money.

The cash register did more for human morality than the Congregational Church. It was a really powerful phenomenon to make an economic system work better, just as, in reverse, a system that can be easily defrauded ruins a civilization. A system that's very hard to defraud, like a cash register, helped the economic performance of a civilization by reducing vice, but very few people within economics talk about it in those terms.

I think there's something to be said for developing the disposition to own stocks without fretting.

If you get into the mental habit of relating what you're reading to the basic structure of the underlying ideas being demonstrated, you gradually accumulate some wisdom.

Even bright people are going to have limited, really valuable insights in a very competitive world when they're fighting against other very bright, hardworking people. And it makes sense to load up on the very few good insights you have instead of pretending to know everything about everything at all times.

The tradition of always looking for the answer in the most fundamental way available - that is a great tradition, and it saves a lot of time in this world.