If stock price movement is some kind of stationary process , trading is much easier for everyone. But it is impossible for everyone to be a winner. Most are losers. If the stock prices are not any kind of stationary data, how much things like TAs and highly hyped ML skills are really useful and effective in trading? Trading is a myth not a science. Winners are mostly created by legal and/or illegal privileged access to machines, information or techniques (short-lived if open to public). Just my random thought (or repeat of others said).