Here's the thing. You're 25. You're total investments now add up to only a teeny tiny fraction of the amount that you will invest over the course of your lifetime (no offense, I'm sure it seems like a lot of money now). Sure, imaging the worst bear market you can think of: Say it's 1929 and the markets are plummeting. You won't retire until 1969. Yes, you'd lose money on your investments for the next few years (I'm not a market historian--somebody help me--when did the markets hit their nadir? 1933?). But if you continue to invest while the market is down, you are "buying low" and by the time you retire you'll be able to "sell high." Remember that most of the money you will invest in your lifetime you haven't earned yet.

Bear markets teach you your risk tolerance. Queasy? Maybe you need to turn down your risk exposure. But don't let a bear market frighten you out of the market entirely (or at least permanently), because you'll miss a whole heck of a lot of opportunity.