NEW YORK ( TheStreet) -- A good friend of mine, an industry veteran, has historically described market ups and downs as the "oscillation between greed and fear", as it applies to investor psychology.Despite the fact that I've given him a lot of ribbing about that term over the years, there is a lot to be said for what it conveys. In a nutshell, when the markets are continually heading higher, investors can become greedy, leading them to pay too much for securities. When fear sets in, and markets fall, investors tend to sell to a level in which securities prices are punished far beyond what they deserve. You can certainly apply that logic to individual stocks, as well. Green Mountain Coffee Roasters ( GMCR) is a great example of the "greed" factor. While Keurig machines and K-cups became quite a phenomenon over the past few years, investors got a bit too greedy with the stock, pushing it from about $9 in January 2009, to more than $100 by August 2011. While the company's growth was explosive, the stock price got ahead of itself, and the multiples became ridiculous. Concerns over accounting issues, and slowing growth helped to send shares from around $108 in August 2011, to $44 by the following November. By last July, shares had fallen to $18, before rebounding to $40 recently. Investors who bought in because of the single-cup coffee craze, but ignored valuations got hurt. I've never been a big fan of the single-cup phenomenon, primarily due to the expense; in fact I still think it's a fad. Admittedly, those who took positions in Green Mountain early in the summer have doubled their money; taking advantage of the fear that had set in. It remains to be seen how this story will end. Krispy Kreme Doughnuts ( KKD) provides an interesting example of fear. The former cult stock had languished for years following mismanagement, over-expansion, and accounting issues. In recent years, the company has quietly put its financial house in order, rebounded, and is growing again, primarily through international franchising. But for years, investors avoided it, and with good reason.