Essentially it means you can’t make money, without one of the following (1) luck or (2) non-public information.  Now, to be precise, the phrase “you can’t make any money” really means, “you will not consistently achieve risk-adjusted above market returns.”  And by “you” I do mean YOU, whether you’re a Harvard undergrad day-trading in your dorm, a retiree with a 401K, or  you’re running a $10 billion mutual fund or hedge fund.