I don't doubt that you, specifically, may have beat the S&P, but I think lots of people don't keep a great track record of how they've done, tend to forget their average or bad trades, and overemphasize their good trades in their minds. I'll then ask them how much their overall portfolio has grown from year 1 to year 5, and then calculate the S&P's growth in that time, and they almost always have only managed to match it (with a lot of time wasted to do so) or actually did worse.
Ha! This is true for me, I only realize how much I've lost when I see those negative numbers in TurboTax before filing my tax return.
It is possible to win, but you need to be good, and most people who do it in their part time simply don't have the knowledge or experience required...
Keep in mind that when you're playing the markets, you're competing against institutional investors and hedge funds that have far superior resources (data, algorithms, etc) to better analyze the market and to even move the market in a direction favorable to their holdings (e.g. Warren Buffet). The most likely outcome of trading is that you'll get out-gamed by these sophisticated investors.