Imo the mistake most make is they mentally compare it to themselves reading a bit online and then picking stocks based on what they feel will perform well. Of course this can only go wrong. If you're an expert in an area like the first quant traders or someone who understands startups and does angel investing, you can absolutely beat the market and people do it all the time. That's how some people get rich, you can not become truly rich by working a 9-5 office job and buying a few stocks. Unless theoretically you trade the riskiest penny stocks with leverage and magically come out on top every time like some of those WSB guys. I've yet to hear of cases where this works long term. The smartest ones know when they get lucky and stop playing, because that's pure gambling.