The difference compounded over a long period of time is a lot of money.
If you put all your chips on 'red 39,' of course you're going to win from time to time, ... Obviously you get periods when active managers look like they're adding value, when they're really just in a different part of the market.
If you're 22 and just out of school, you can afford to make a risk because you'll have a lot of time to make it up before you retire. For somebody mid-career, you can take a chance, but if you do that, you have to protect your investment capital -- your IRA and your other savings.