I remember the first time I sat down at a real poker table in a casino. I had occasionally been playing online (mostly with pretend money) over the years, and felt that I had it pretty well down to a science. A numbers game. I knew what to do with whatever happened. But the first time I sat down in person, everything was different. I froze up a lot, got confused and distracted. But I also felt like I had less patience because real-life games move way slower than online games (and yet seemed more confusing, heh). And you only play one at a time. Because I had less patience, I wanted better hands sooner than later, and I felt more inclined to raise when I should just call, and so on. It is a lot harder to play disciplined poker at a casino than it is online. Experienced in-person players understand this and will use this to their advantage when the can sense greed in new players.
Obviously what a person has to do is put in comparatively many hours at the real-life tables as the online ones. This requires a lot of time and money, though, not to mention patience. And the more time you spend doing something addictive, well, the more likely you are to end up fucked in some way.
Another thing to worry about is drugs in casinos. If you don't think that almost every large casino has drug dealers roaming them, you've just not learned how to recognize them yet. Poker players love benzos in particular to make those grueling shifts bearable. And a lot of casinos feed people free alcohol as long as they keep gambling. If you get into the habit of drinking, taking benzos or something similar while gambling, you're going to have to try and walk away from multiple bad habits.