I often hear authors advocate discipline — “Set your own rules and follow them consistently.” However … Q: why do we need to monitor the market rather than program a computer to do so?

More importantly… Q: how do I know when to turn on manual override and modify my rule?

I think in reality, what we can realistically do is “Follow personal rules 95% of the time” What percentage of retail investors have the discipline to achieve that? One in 10? Among this subset of (millions of) investors, their numeric rules are all different and therefore create millions of “free agents” that power the free market.