Let's say, back-testing is the first step. I currently have a RSI system, runs well in back-testing. Then, I go to the second step. Put it in a demo account to see how it works, the difference between back-testing and real trading. Finally, I still need to modify the system and let the computer do the trading. The market is so drastically when the news comes out, hand work doesn't work. The market is always change. That's right. But the fundamental that makes the market change is changing slowly. That's why we learned the past and predict future. Like a trading system, it could be runs well in the last 10 years, because it is just fit. We should assume it will runs well in the following 10 years, if not always(greater than 10 years). What we should do is to abstract in a year frequecy. Traders is always trying to find a system that earn as much as possible, try to approach the limit (if the limit exists). But in my view, make enough money for a good living is enough. Life is not just trading. Spend half hour on personal trading each day is good. More than that, very bad.