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.