David Slansky coined the term “the gap” to describe the distance between the hand you need and the minimum opening hand. Put in its simplest terms, it refers to the fact that the stronger your read on your opponent’s hand, the wider the space is between your minimum opening hand and what the calling hand would be under the changed circumstances.
In other words, you must have a stronger hand to call than you would need to open the pot yourself from the same position. In Texas Hold ‘Em, part of a player’s incentive to open up the pot is the chance that opponents will simply fold their hands in response, giving you the chance to pick up the blinds without any kind of showdown. However, if there are already players in the pot by the time the play reaches you, that possibility vanishes entirely.
You’ll want to bear in mind that the player who opened ahead of you did some from an earlier position in the game and thus must have a stronger minimum hand to open than you would from your position. Further complicating the moment is the fact that you have no idea if he opened with a stronger-than-normal minimum starting hand or is actually holding a monster hand and attempting to get some fish on the line.
In a situation like the one described, it’s reasonable to assume that you are, at best, a solid underdog with one of your minimum starting hands and that you’ll need some help from the board to make do. This means that you’d need to have significant pot odds to make calling worthwhile.
Let’s use an example from a game that I recently observed over while looking over a friend’s shoulder as he played online. He was in late position with A9, unsuited and everyone was folding until they got to the fourth guy in the rotation, who raised on the flop. What was at first glance an eminently playable hand became a bit of a burden as I walked him through folding. If the cards had been suited, perhaps, he would have stood a chance, but I had to break the bad news to him.
Once they begin to understand and use the gap, a lot of the money that newer poker players bleed out early on in their hands finds its way back into the bankroll.