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There's a riddle Goldman Sachs has asked job candidates where the right answer is to eat the poison, and it only works because there are 253 lions in the room instead of 254. The setup goes like this. There's one poisoned steak, and any lion who eats it falls asleep. A sleeping lion is fair game for the rest of them, and whoever eats him falls asleep too. Every lion is perfectly rational and wants to live. The trick is to forget about 253 lions and start with one. If there's only one lion, he eats the steak, takes a nap, and nobody's around to bother him. With two lions, nobody eats. Whoever goes first passes out, and the other one gets a free meal with nobody left to come after him. With three lions, somebody eats. Once he's asleep, the other two are stuck in the two-lion situation, where taking a bite means you're next, so they leave him alone. He ate the poison and he's the safest lion in the room. Four lions, nobody eats, because the first one to bite leaves three behind, and we just saw that one of those three will happily eat him. Keep counting and the answer flips with every lion you add, so all you really need to know is whether 253 is odd. It is. One lion eats, and the other 252 spend the night staring at a sleeping lion every one of them has figured out they can't touch. What makes this a Wall Street question is how much trust the answer takes. For lion 253 to eat safely, he has to know every other lion is perfectly rational, and know that they all know that, and so on, 252 layers deep. He's betting his life that the lion at the far end of the room did the exact same math. Actual humans tap out after two or three layers, and somebody measured it. Back in 1997, Richard Thaler got the Financial Times to run a contest. Readers picked a number from 0 to 100, and whoever got closest to two-thirds of the average won two business-class tickets worth over $10,000. Follow the logic all the way down and everyone should pick zero. The average came in at 18.91, which made 13 the winner. The two most popular guesses were 33 and 22, which is what you get from thinking one and two steps ahead. Plenty of people did the perfect math, wrote down zero, and lost to people who just had a good read on how far everyone else would bother to think. Keynes said the same thing about the stock market back in 1936, that you make money by guessing what the average investor thinks the average investor is going to do. A Goldman quant told eFinancialCareers the lion question was the easiest of seven riddles she got in a single hour, which tracks, since the math only gets you hired. Once you're on the desk, the money comes from knowing the person on the other side of your trade probably stopped thinking somewhere around 22.