for all games, including Black Jack, but especially Poker!
If your game has not improved over the past few years (not saying it hasn't), it stands to reason it will effect your net outcome. What might have gotten you by in the past might no longer be as effective today with the quality of play at the tables now. I've been playing Poker for over 40 years, and I can see at just about every place and level I play today a much more experienced and skilled crowd at the tables, especially with the youngsters.
They are fearless and aggressive, and with so many books now on poker out there to help educate the novice, along with online poker for practice, whether play-money or not , they gain more game experience playing one or two weeks on-line than it use to take us old farts months, even longer.
And what the previous poster said about the increased "rakes" has an awful lot to do with it too!
Just my two cents worth!