I'm a undergrad in biology. I'm long AAPL ALSN LVS TCK LUK and some mutual funds. I've been an investor in mutual funds since 2002, but found to dislike like the +/-gains. My first 'almost' double bagger was CAT. I held BP through the whole oil spill only to sell at mere gain. I don't short or play options. Sold: CENX 2.6 bagger; MUSA at 40% gain after spin-off dividend from MUR; KCG 26% gain after holding for 2.5 years. ACI 99.95% lost... just couldn't sell after 75% of my money just vanished.
Peter Lynch said "There is always something to worry about. Avoid weekend thinking and ignore the latest dire predictions of the newscasters. Sell a stock because the company's fundamentals deteriorate, not because the sky is falling."
Warren Buffett: I say hold, basically hold. I mean, the idea that the European news or slowdown in this or that or anything like that, that would not cause you to own a good farm and had a run by a good tenant, you wouldn't sell it because somebody said here's a news item, you know, this is happening in Greece or something of the sort. If you owned an apartment house and you got to raise your rents a little, it's well located and you have a good manager, you wouldn't dream of selling it. If you had a good business personally, the local McDonald's franchise, you know, you wouldn't be thinking about buying or selling it every day.
I am a reformed MD, now with a finance MBA, and studying valuation independently by developing some conservative DCF models using FCF per share. You can make any investment work if you set a low enough discount rate.... that's one of the discouraging things about doing anything other than passive index investing. Forecasting isn't too accurate, those darn standard deviations are too wide. Margins of safety and alpha are rare and hard to separate from the noise.