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.

The interesting thing is the field is so big - it's enormous. One thing a modern civilization needs is energy.

The idea of excessive diversification is madness. Wide diversification, which necessarily includes investment in mediocre businesses, only guarantees ordinary results.

After nearly making a terrible mistake not buying See's, we've made this mistake many times. We are apparently slow learners. These opportunity costs don't show up on financial statements, but have cost us many billions.

An idea or a fact is not worth more merely because it's more available to you.

The only way to win is to work, work, work, work, and hope to have a few insights

There are two kinds of businesses: The first earns 12%, and you can take it out at the end of the year. The second earns 12%, but all the excess cash must be reinvested - there's never any cash. It reminds me of the guy who looks at all of his equipment and says, 'There's all of my profit.' We hate that kind of business.