|>>|| No. 5023
The world is full of professional traders, whose job is to profit from market fluctuations. They have access to huge informational and computational resources. The only way you can beat them in the long run is to know something that they don't.
Imagine you're playing roulette. In the short-term, you'll sometimes win and sometimes lose, but in the long-term, the casino will always win out, because the odds are stacked in their favour; A European roulette wheel has 37 numbers (zero to 36) but pays out at 35/1, giving a house edge of 2.7%. All sorts of people believe that they have a 'system' that allows them to profit at roulette, but that's mathematically impossible unless you're actually cheating.
Small investors lose out in two ways - firstly, that they have much less knowledge than professional traders, and secondly that a relatively large proportion of their capital is lost to brokerage fees. Unless you have some sort of insider information, it is provably true that the best investment strategy is simply to take a diversified position (investing in a broad range of shares and bonds) and to hold that position indefinitely.