> So when you notice a pattern - say "Stock S trades lower on Tuesdays and higher on Fridays", what do you do? Do you buy on Tuesday to exploit the pattern? Or do you buy on Friday because you are not a unique snowflake and others will notice the same historical pattern and therefore reverse it in the future?

Why would you expect it to reverse?

If anything I’d expect the pattern to disappear once detects and arbed away.

I can’t see how you’d think the pattern would reverse itself.