Humans crave that kind of structure, probably because we get so little of it in real life. It's a lot harder to say whether you "have a healthy romantic relationship" or "are making a lasting contribution to something bigger than yourself" than that you've "lined up the yellow gemstones," "scored more points than the other team in twenty minutes," or "collected forty pounds of silver."

Think of the pleasure we get crossing things off lists, the thrill of reaching "inbox zero" or finishing a book. We want to accomplish things and, maybe more importantly, we want to know that we've accomplished them.

Games (and video games in particular) exploit that essential insecurity. They're engineered to unfold as a series of short feedback cycles, every action a small experiment that concludes in minutes, if not seconds, with concrete consequences: you either win or lose points. That vivid loop keeps you constantly engaged. It sucks you into the micro-mechanics of the game, because even the smallest maneuvers give you the feeling of "getting somewhere." You can't help but tweak, tweak, tweak your way up the game's learning curve, an eye always on your rising score.

Now think of what a trader does. A trader's job is to be smarter than the market. He converts a mess of analysis and intuition into simple bets. He makes moves. If his predictions are better than everyone else's, he wins money; if not, he loses it. At every moment he has a crystalline picture of his bottom line, the "P and L" (profit and loss) that determines how much of a bonus he'll get and, more importantly, where he stands among his peers. As my friend put it, traders are "very, very, very competitive." At the end of the day they ask each other "how did you do today?" Trading is one of the few jobs with an actual leaderboard, which, if you've ever been on one, or strived to get there, you'll recognize as being perhaps the single most powerful driver of a gamer's engagement.

That seems to be the core of it, but no doubt there are other game-like features in play here: the importance of timing and tactile dexterity; the clear presence of two abstract levels of attention and activity, one long-term and strategic, the other fiercely tactical, localized in bursts a minute or two long; the need for teams and ceaseless chatter; and so on.

Not to mention that the whole job takes place indoors in a kind of software cockpit driven by people sitting in a climate-controlled room staring at screens scrabbling away on colorful complicated keyboard controllers.

Mind you, the game the traders play is nothing like Mario or Zelda or Megaman. It's not a shoot-em-up or racing game. What it is is more like Starcraft or maybe TradeWars: an intense, cerebral, massively multiplayer real-time strategy game. It's a game grounded in information: prices, mostly, but also all kinds of news and rumors and oblique signals, whether by way of balance sheets or CNBC. It's the kind of game that requires the player to immerse himself in data, distill from it a sort of strategical gestalt, and convert that high-level battle plan into a series of discrete maneuvers, in this case trades on the open market.