What “markets are efficient” means is really that you can’t make more money on the stock market than average unless you put the same time and brain power to it that hedge fund people do, and even then you can only make about as much money as hedge fund traders do. (Assuming a few things, like that you’re only trading based on public knowledge)

The logic is this: if this were not the case, then some of those very smart hedge fund people were take advantage of this strategy, making that strategy become the average that everyone wants to beat.