This is one of the great tragedies of a bear market. It happens every time. And my guess is even more people were affected in the most recent bear market because the decline was so dramatic. Individual Investors pull their money out at the worst possible time and swear off stocks forever. Then they miss out on the succeeding rally or worse they finally decide to buy back in at the very peak. The roller coaster ride starts all over again.
The lesson here is - do not try to time the market! By our nature we are emotional creatures and the only thing to stop us from making mistakes is an investment plan. If you know the cash flows you will need from your portfolio you can put an appropriate amount of money away in high-grade, short-term bonds. This makes you a “patient seller,” gives you the ability to wait out the next bear market and not panic out at the bottom. I am not going to attempt to predict the next bear market, but it will happen. Be ready so you don't get stuck on the next ride.