I have been toying with this idea in my mind for a while now and to me it sounds like a fool proof way of getting 'rich'. I'm sure someone has had the same idea as me, maybe even tried it, and because not everyone is doing it I'm guessing it did not work out very well.
The idea is to make money on small changes in the stock market. From looking at different stocks it looks to me that most stocks go up and down a certain amount at the time. The amount changes, but if there is a positive change in a stock it tends to stay positive for a bit before going negative again.
Could you not write a computer program to track this changes and invest in a stock after it has shown a positive grown for a small period of time and sell again as soon as the change starts to become negative. This would not give a big percentage increase on your investment, but as a computer could track thousands of this trades simultaneously for 24 hours a day I'm sure the overall return could be quite good.
To me the idea sounds fool proof, but I'm sure there are reasons for why people do not do this, I am mainly interested in why. Maybe it breaks trading rules? Maybe you can't buy stocks from a homemade computer program or something else entirely?