But this did not happen in a single, dramatic loss. It was a long, grinding decline stretched out over 21 months. If you invest over a long period, chances are you'll see one or more bear markets. Although the early 1990s saw some brief lagging periods in the stock market, there really hasn't been a sizable or lengthy bear market for over a decade. No one knows when this trend will end, but based on history and the cyclical nature of markets, we can expect that it will end sometime.
Market timing is no more effective in a bear market than at any other time.
But it's never clear that a trend will continue. These drops can set off fears that the market might be heading into a bear period. But in such cases it would be a mistake to sell in order to avoid further decline, because the market does recover. Loss is inevitable. There really aren't any tricks you can play to guarantee the value of your investment won't decline in a bear market.