William Eckhardt: I used to operate under the assumption that although I could never match the performance of tenacious mechanical systems in rare excessively profitable years, I could, by means of experience and judgment, outperform such systems in the more plentiful typical years. In the 80s,I had occasion to have an account traded purely on one of my systems; it out performed my highly discretionary trading for two "typical" years in a row. This experience forced me to reassess my approach. Since1991, my trading has been predominantly mechanical. Earlier I thought the mechanical system is superior in good years, but inferior in mediocre ones.

If you find yourself continually overriding your system, there must be something wrong with your system or with your trading. I advise systematic traders to exercise their ingenuity in their research - not in their trading(other than to finesse order execution).