We found a table Calvin liked. “There are no good pros here,” he said. It was easy to identify the other players at table 24 as fish—the older white guy with gray hair and horn-rimmed accountant glasses was one, and the clean-cut young black guy pushing seven Ben Franklins out of a bank envelope was another. Calvin licked his chops. One of the basic rules of thumb in live poker is that clean-cut young black guys play like older white guys, meaning they are cautious and rarely bluff, which in turn means their hands are incredibly easy to read. According to a handy app on his iPhone called Poker Journal, Calvin has been earning an average of $120 an hour at Maryland Live since the poker room opened. Leaning back in a red-leather-padded chair, he began to figure out whom at the table he should spend his afternoon angling for. “Today I’m going to make my money from those two guys,” he said, nodding first at the black guy, in seat 4, and then at the charter-boat guy, who was in seat 9.

Calvin admitted that there are moments when he feels a little dirty taking other people’s money. He also admitted that such moments are rare. “You need people with money,” he explained. So far, he is winning more than enough to cover his mortgage and car payments, which keeps his wife from getting nervous. “I want to keep those guys in as many hands with me as possible,” he said, “and isolate them in heads-up pots”—one-on-one matchups. “That is my goal for today.”

After three hours of steady losing, the charter-boat guy, whom I’ll call the Captain, was staring down at the eight and nine of hearts—which could have, and by his calculations should have, given him a winning hand. Instead, he lost yet again. “I got the nuts!” he said. “And I still can’t win! Goddamn!” The Captain slapped his cards down on the table with the plaintive cry of a flawed man whose desire to think well of himself is frustrated by realities that defy his understanding. He stared accusingly at Calvin before objecting in a loud, pained voice, “He done got me too many times!”

Most games in which large amounts of money are won and lost require a basic acquaintance with the laws of chance. But poker requires skills that transcend simply knowing the odds of completing any particular hand. It requires a split-screen ability to read the other people at the table while maintaining an awareness of how they are reading you. It requires what is called “leveling”: the ability to move fluidly and accurately in one’s imagination from the hands that all the other players are representing, to the hands that they probably have, to the hand that they think you have, to the hand that they think that you think that they think you have. The acute awareness and processing ability required to quickly go through a complex checklist and get it right—while controlling your thoughts and behavior so that others can’t read you with any equivalent degree of accuracy—is what separates poker pros from casino operators and other crude types who profit from the fact that large numbers of people are dumb or drunk and can’t do math.