In the Texas style of hold'em poker, each player is dealt two cards. A large part of strategy in the game revolves around figuring out which two cards your opponents are likely to have. Using a type of mathematics called combinatorics, you can use the cards you are dealt and the community cards to figure out how likely it is for your opponent to hold different starting hands. This information is absolutely critical and using it effectively will give you a huge advantage over other players at the table.

Suppose you're dealt a flop with only one other player in the hand and it comes QJ4 with no possible flush draw. Here you're often going to be considering betting the flop as a bluff, but you could be scared that your opponent might have AA or KK. If you count up the different ways your opponent could be dealt cards to have a pocket pair, the suit combinations possible are spade-heart, spade-diamond, spade-club, heart-diamond, heart-club, and diamond-club. This means that there are six ways for your opponent to have AA or KK each, for a total of 12 ways for them to have it.

However, suppose you hold AK of spades yourself. The situation is now completely different. Every possible AA or KK hand that holds a spade is now impossible for your opponent to hold because you hold the Ace of spades and the King of spades in your hand. If you count out the suit combinations, you'll see that your opponent now only has three ways to have AA and three ways to have KK, for a total of six ways to have an overpair. By holding AK, you have blockers to AA and KK, which drastically reduces the chance that your opponent has an overpair on this board. If they're less likely to have a good hand, that means they're folding more often, and your bluffs will be more profitable.