Remember, the stock market is a zero-sum game Actually, it's a negative-sum game when taking investors costs into account, but in essense, for every winner there is an equal and opposite loser in the stock market. Those who sold REI at the bottom are the losers, and the winners were the ones who gobbled up the losers' shares at a bargain price.
The key to successful value investing is temperament, not intelligence. Don't panic when stocks crash and proceed to sell at the bottom. Be patient, wait for value opportunities, and don't be too quick to sell when you see your undervalued stock purchase rise in value. Wait until the stock is no longer undervalued and then proceed to sell. In the case of REI, I recommend waiting to sell next year when it hits $24, at the very earliest, and from there move on to the next undervalued opportunity.
Good luck to everyone.