I think everyone leaves money on the table at some point... but if you are careful, when it's time to lose money, you don't lose as much either, so your attitude can be really beneficial as well.
I try not to buy anything that will drop much, based on fundamentals, and I sell based on momentum. It won't make you feel better, but I still have some stocks purchased in 1999 and 2000. They're the ones beginning to make some moves, but it's a long long way back up (CSCO from $72.50 for one specific... so any upside for me there is nothing). For me, they are bellweathers, and a lesson I have to look at every day when I think I had a good day.
Here's the crazy part. I frequent this forum because I think by osmosis I'm going to get interested in technicals and better at gauging fundamentals. I have read several books on TA, and they just bored me silly. Fundamentals? That's not a good predictor either, Microsoft and TWX have pretty incredible fundamentals, but they don't move much.
I trade on gut feeling, news and logic, as I can't find anything else that's reliable. Ie, when everyone was screaming recession, I thought the market was trying to shake the insecure people out of the trees for a huge move up. I went all long, and in tech no less. I know no one has anywhere else to put their money but the stock market. How can it do anything under these circumstances but go up?
Don't regret your profits, 33% is a hella lot better than Treasuries and CD's

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I will say that I'm very shaky for January. My gut tells me we're in for a good sized correction (I read buying opportunity) some time mid January... but not Dec.