The online poker boom of the early 2000s changed the way the game was played in brick and mortar casinos in lots of ways. We can discuss all of them in the comments, but the reason I bring it up today is that playing online allowed poker players (especially younger ones) to get a lifetime's worth of hands and experiences in less-than-a-lifetime's worth of time. So you had older players who had "seen it all" playing against guys who literally had seen it all - enough hours, enough repetition, enough hands and pretty soon you know exactly what to do when someone floats you on the flop and turn and triple barrel shoves on a seemingly-bricked river because you've seen it hundreds of time instead of once.