Somewhere along the way, being flexible in the stock market–i.e., selling quickly if you develop a loss, or changing your mind just a couple of weeks after buying a stock–has gotten a bad rap. If you change your mind, you’re derided for being a “trader,” or for not having any conviction. Nonsense! While conviction is important, so is being flexible. You must always be willing to change your outlook–if the market or your stock dictates it. Corning (GLW) provides a perfect example. We added GLW to the Cabot Market Letter‘s Model Portfolio back on May 7. At that time,...