Ron Vinder, a financial advisor at UBS Financial Services, says he’s doing just fine by managing client portfolios with a broad set of ETFs. Rebalancing the mix is a critical part of the strategy, he explains via Barron’s. “Whenever an asset class does well, that’s when individuals want to buy more. And they want to sell what’s doing poorly.” That’s all too typical, of course, which is part of the reason why the expected premium from rebalancing is so attractive. Indeed, if everyone was diversifying broadly and opportunistically rebalancing, the performance advantage would shrink considerably. But don’t worry: crowd behavior is resiliently rigid—even when the evidence for change is overwhelmingly persuasive.