In his annual letter to shareholders which you should read here:
Investors, of course, can, by their own behavior, make stock ownership highly risky.
And many do. Active trading, attempts to “time” market movements, inadequate
diversification, the payment of high and unnecessary fees to managers and advisors,
and the use of borrowed money can destroy the decent returns that a life-long owner
equities would otherwise enjoy. Indeed, borrowed money has no place in the investor’s tool kit: Anything can happen anytime in markets. And no advisor, economist, or TV commentator – and definitely not Charlie nor I – can tell you when chaos will occur.