A skilled poker player tends to win in the long run. There are only a few exceptions:
1) That he moves up levels and ends up playing at a level where he has no edge. Therefore, assuming he manages his bankroll well, he has to go down a level.
2) He is going through a bad psychological moment in his life, which leads to alcohol or drug consumption and that affects his gambling.
3) In the case of big tournaments played live, the variance can last for months or years without significant results. Thus there have been a few players who quit the modality or poker altogether.
But a winning NL100 SH player, settled at the level for years and who wins at 6bb/100h, and hasn't dabbled in alcohol or drugs is always going to win in the long run.
You are thinking of a professional poker player, but not all poker players are professional, so the one that wins on the long run is a guy like Phil Helmut or Daniel Negreanu or Phil Ivey. Of course, those people will always end up earning some money when they get in, hell they are offered entry fee by others, just to share the winning pot if they win, meaning they may not even have to pay for anything anymore, they either win something or win nothing but not even lose anything.
So, if I start gambling poker, I would be terrible at it, and would lose in the long run, but those famous poker players would win, there is a big big difference.