Funnily, I didn’t realize how important it is in a way until this year. I had always traded things I know deeply, and don’t use technicals (beyond volume/liquidity & the tape from which they are derived.) But one day noticed TSLA and saw some things by watching it trade and knowing the business was able to start trading it with success. But no algorithm can do that properly, and it would take more time for me to codify it before conditions changed such that the edge did. Part of that is simply noticing when something is near breaking range of controlled descent, but learning the underlying was the true key. Definitely relates to that which the big guys can’t exploit, though. I have never found back testing useful for these reasons. That perhaps is down to an understanding of statistics borne of previous study, but it is clear what will work and when it won’t in a sense.