Sell reluctantly and don't panic. Corrections create opportunities. You wouldn't want to buy always at the market highs. All stocks eventually have a selloff period, regardless of how great an investment the company may be. Be patient before you add more to your positions.
Stocks are the one thing that no one buys when they go on sale.
If you believe in the company, buy more when Wall Street has a fire sale or falls out of love with your company. But always reevaluate why a stock has become cheap. There may be a reason other than the typical emotional market whims. Be true to yourself and ask some tough questions. Compare this investment to others that are doing well in your portfolio.