Over the years I met a couple of dozen of (human) traders who I'd consider good (being in the business for several years, generating a reasonably steady income). I had chances to chat with some of them regarding their trading strategies. All of them admitted they are not doing anything "out of the ordinary", whether it's some sort of pairs trading, trend following, curve fitting, and such.
Since these techniques are well known, I'm wondering why are they (still) able to generate profits? Is trading some sort of a CAPTCHA, one that machine-learning or other algorithms unable to crack?