Ah, but you're talking about short-term luck ("I sat down at a table full of sharks", "I sat down and was too tired to play my best"). On any given day, you can win or lose, and the best player in the world can't guarantee a win across a short period of time. That's the strong gravity of short-term luck in poker.

But sit down and play 5 or 10 million hands online (that's under a decade of regular play, well within a human lifespan), or even considerably less than that, and luck becomes a rounding error. Mathematically. Incontrovertibly. Your long-term results in poker will reflect your skill level closely. And of course the rake plays a part as well, by turning poker into a negative-sum game instead of a zero-sum game, and dragging everybody's results slightly south of where they would have been otherwise.

But rake or no rake, there's very little "luck" in poker at depths of millions of hands, as you get in today's online games.

And even in the live game, where hand throughput is lower, luck is a small enough factor over the years that the same skilled players win consistently, and you can only win consistently by learning those skills.