From investor Howard Marks’s interview at The Wharton School, University of Pennsylvania:

There’s no such thing as analysis of what’s coming. We don’t know anything about the future, and you can’t prove anything about the future. But if you’ve been in business and you’ve seen some cycles, and you’ve gained some experience and you’ve gone through those cycles with your eyes open saying ‘What are the implications of cycles for our behavior?’, then I think you can reach a point where you say, ‘You know what, it just feels like the power is in the hands of the issuers, not the buyers. It feels like there aren’t many sellers, just a lot of buyers. And the market is not acting in a disciplined way.’ We want to buy when the market in panicked, not when the market is sanguine. Buffett says that ‘The less prudence with which others conduct their affairs, the greater the prudence with which we must conduct our own affairs.’ When other people are optimistic, we should be worried. When other people are panicked, we should turn aggressive.

Source: YouTube Video – Howard Marks at the Investor Series at The Wharton School