I'm not sure I agree with this 100%. If this were true, an investor like Warren Buffett, who has always invested by focusing on the fundamentals of the company he is investing in and focusing on real performance/value metrics, would not be able to be as consistently successful as he has been.

It's hard to say though, because the market in which he made his initial chunk of capital is not the same market today, and it's impossible for me to parse out the self-reinforcing effect of "price goes up because Buffett has taken a large stake" versus the sort of fundamentals I'm referring to.

edit : Having said that, I do believe there is a class of people who are able to make money off of the stock market in a way totally unrelated to the reality of the underlying instruments - profiting on churn, market-making, small percentages on massive positions, etc. But I don't think that means the underlying instruments are actually worthless/not tied to real value.