If we read up on complex system theory we find that the law of requisite complexity means that a controlling system [in our case the market] would have to be equally or more complex than the controlled system [our strategy]. This raises some questions and I think that the most important one is of complexity of a market. If one views a market as more complex than it really is, his strategy is likely to have too much complexity in it. If one views a market as less complex than it really is, efforts to keep one's system even simpler than one's view of the market could result in a system that is too simple. I've seen posts on ET wherein a system trader had a system that worked for years and then gave it all back and more in a month. That would be an example of underestimating the complexity of a market. I've seen lots of posts saying that systems are all random over enough time. That might be an example of overestimating the complexity of markets... I'm sure that fundamentalists are overestimating the complexity of markets if they are not holding for a long time. My new definition of "market" is: the minimum that I need to know about a market in order to trade it. It's like Einstein said: "Make things as simple as possible, but not simpler". My new definition of a trading system involves making sure it is complex enough but not a bit moreso. Does this resonate with anybody?