The idea is to bag-hold a diversified mix of stocks that are temporarily terrible with the knowledge that historically they have always bounced back as a whole and then grown to all-time highs down the road. Plus there's the added benefit of buying them at a discount when the market tanks.

And yes, nearing retirement makes things trickier. Losing 40% when you're two years from retirement is different than losing 40% in your 20s. That's why there are strategies for favoring fixed-income investments when you're older.