When to sell: It's the age-old investing question. Berkshire Hathaway (NYSE: BRK-B) CEO Warren Buffett says his favorite time frame for holding a stock is "forever." Investing great Peter Lynch says you should sell a stock when your reasons for buying no longer apply. And legendary fund manager John Neff says it's "probably time to sell when you feel like bragging."  

Motley Fool co-founder David Gardner has racked up some big returns for investors by recommending stocks such as Amazon.com (Nasdaq: AMZN), Intuitive Surgical (Nasdaq: ISRG), Marvel (Nasdaq: MVL), Netflix (Nasdaq: NFLX), NYSE Euronext (NYSE: NYX), and Take-Two Interactive (Nasdaq: TTWO). At a recent Washington, D.C.-area Motley Fool community event, David shared his thoughts on when to sell.

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