Win rates in big bet poker games overwhelm variation quickly. You absolutely will know if you are a big winner or big loser. If your results hover around breakeven - then sure, you will not be able to tell if you are a slight winner or slight loser.
The lore about needing tens of thousands of hands to know how much you do or don't win comes from limit poker. The win rates are very thin in limit poker while the variance is only slightly smaller than big bet poker.
Examples:
Let's take a big bet poker game. A solid winning player makes 20 big blinds per hour. Let's say he was a bit laggy so his variance is also 20 big bets per hour. Some hours he kills the game - 5% of the time he will win 60bb in an hour. 5% of the time he loses 20bb in an hour.
win rates are linier. you win / lose your rate every hour on average. But the variance grows with the square root of the time spent playing. At the end of a four hour session our winning player above has made ( on average ) 4 hours X 20BB per hour = 80 BB. But the variance will be (sqrt of 4) = 2 X 20BB - or - 20BB for the session. This player only has one losing session every twenty nights. See? Its obvious this player is a big winner with less than a hundred hours.
Let's cut the win rate to 10BB/hr while keeping the variance at 20BB/hr. For this player, a four hour session looks like this - wins 40BB on average. Break even or worse a third of the time. +80BB or more a third of the time.
So what does this look like at a hundred hours? Average win rate = 1,000BB (10BB/hour X 100 hours = 1,000BB) Variance is 200BB per hundred hours played. ( 20BB/hr X (sqrt 100) 10 = 200BB per hundred hands. The chance of this player having a random breakeven or worse result after playing a hundred hours is vanishingly low - something like 3.5 million to one.
Bluntly, a significantly winning player that suddenly stops winning for any substantial time is NOT bad variance or bad luck. Its bad play or the player pool got much tougher or maybe the player is suffering from an illness. yeah, yeah, I have seen the hand histories, the bad beat examples blah, blah, blah. Very pretty graphs to be sure. But math doesn't lie. If someone's win rate plunges over a month or two in a weekly game, it is primarily due to poor play or tougher villains or both.
One bad night easily happens. A bad month ( playing weekly) rarely happens. A bad year is unthinkable for the 10BB+ win rate player. Not once in a typical lifetime.
DrStrange