Set

You're in the cutoff with 5♦5♣ and call a raise from under the gun. The flop comes K♠7♦5♥. You've flopped a set of fives — three of a kind nobody can see coming. Under the gun leads out with his king, sure he's ahead, and you're crushing him.

That invisibility is the point. A set doesn't show up in your preflop action — small pairs call, they don't raise, so nobody puts you on one. So they pay you off: a player with top pair or an overpair keeps firing into a hand that already has him beat. The catch is you rarely flop one. Hold a pocket pair and you hit a set on the flop about 12 percent of the time — once in eight or nine — so most small pairs go in the muck unimproved.

Beginners lump the set in with any three of a kind, including the kind made from a paired board plus one card in your hand. That's trips: weaker and easier to read, because the pair sits face-up on the board for everyone to see. Confuse the two and you overvalue trips as if it were as hidden as a set, and you underplay a real set because the board looks safe. Know which one you're holding before you decide how hard to bet.