Jeremy Grantham’s latest missive(.pdf) is well worth a look if for no other reason than it provides some excellent discussion about financial bubbles through history, the most compelling being Isaac Newton’s disastrous participation in the 1720 South Sea Bubble.
Newton had the great good luck to get into the South Sea Bubble early. He made a really decent investment and a very quick killing, which mattered to him. It was enough to count. He then got out, and suffered the most painful experience that can happen in investing: he watched all of his friends getting disgustingly rich. He lost his cool and got back in, but to make up for lost time, he got back in with a whole lot more (some of it borrowed), nicely caught the decline, and was totally wiped out. And he is reported to have said something like, “I can calculate the movement of heavenly bodies but not the madness of men.”