Traders often wonder why anyone would want to sell a good trading system to the public. The amount of money the developer of the system could make from trading the signals would potentially be so much more than the relatively small amount of money received from the sale of the system. Other traders are concerned with the effect of revealing the secret rules of the system to the public, which could possibly ruin the performance of the system. These are some of the reasons that many traders are skeptical about mechanical trading systems.

There are people selling products of dubious benefit to the public but this happens in any business, not just in the trading industry. There are definitely some bad trading systems which will not make money, and others whose secret is not far from the fairly well known and simple moving average systems. It is also true some methods have become so well known that the system has lost its effectiveness for a variety of reasons. For example, widely followed trading methods can produce a bunching of stop orders at the same price level, which can lead to terrible fills. Another problem with a system becoming too popular is that if too many people use the system, the signals will tend to lose their validity.

There are good trading systems which are developed by sincere people who mayor may not choose to trade them. Some people are good theorists but do not apply the theory well. A close analogy occurs in science. Physicists work in a theoretical world and think about all kinds of ideas, but do not usually apply the ideas to real world applications. The engineer works with the theoretical idea of the physicist and applies it to practical use. The same may hold true in trading. System developers may create good trading systems, but they may not be able to trade them for many reasons. Traders must be practical, and may be able to apply the ideas of the system developer to the market.