Which thinking habit do you wish you could break?

Ironically, though, this is also the purchase in which I made my biggest mistake - of a kind, however, never recognized on financial statements. We paid $600 million in 1989 for Gillette preferred shares that were convertible into 48 million (split-adjusted) common shares. Taking an alternative route with the $600 million, I probably could have purchased 60 million shares of common from the company. The market on the common was then about $10.50, and given that this would have been a huge private placement carrying important restrictions, I probably could have bought the stock at a discount of at least 5%. I can't be sure about this, but it's likely that Gillette's management would have been just as happy to have Berkshire opt for common. But I was far too clever to do that.