Lessons From the Recession
Millions lost their homes, savings and jobs in 2008 when the economy went into free fall. What have we learned?
Lynn Brenner, AARP Bulletin, September 2013
In particular, see #3:
The big challenge in such a market is resisting the overwhelming impulse to join the stampede for the exit. History has repeatedly shown that sitting tight is the key to successful stock market investing. If you sell, as many people did in 2008, you lock in your losses. That's a disaster....
... assume that your stocks... can drop 50 percent ... and stay down for a very long time.... (The average bear market since 1900 has lasted about 14 months, with an average decline of 31.5 percent.)"
link-
http://www.aarp.org/money/investing/info-08-2013/lessons-from-the-recession.print.html