In the video James H. Simons: Mathematics, Common Sense and Good Luck, James said that the only rule (in Renaissance Technologies Co.) is too "never override the computer" (See between 49:00 and 49:20). Could anyone be able to explain what it means and what it is the case?
Simons is talking about his company, which uses quantitative methods to automate financial trades of various kinds. "Overriding the computer" means making a trade other than what the computers are currently programmed to make, or preventing a computer-scheduled trade. The reason, Simons goes on to say, is that statistically analyzing the company's performance becomes much harder in the presence of human whimsy affecting the company's trades.
This is closely related to the issue of actuarial (quantitative, automatic) versus clinical (qualitative, manual) decision-making that's considered in psychology. Not surprisingly to a statistician, actuarial methods perform better than clinical methods, and purely actuarial methods perform better than actuarial methods with optional clinical overrides. See, for example,
Dawes, R. M., Faust, D., & Meehl, P. E. (1989). Clinical versus actuarial judgment. Science, 243(4899), 1668–1674. doi:10.1126/science.2648573