The most costly error that you can make is to fold a hand that has a strong chance to win a large pot. This error is so costly because it theoretically costs you a large fraction of the pot when you make it. That is, if you have a forty percent chance of winning a ten bet pot, folding on the end for one bet rather than calling costs over three bets (3.4 bets to be precise, the four bets that constitute your forty percent share minus part of the bet you saved by not calling). Compare this to the error of calling when you should fold. Even with no hope of winning, calling costs at most one bet.
The fact is that most small stakes players rarely make this error. In a large pot most people instinctively see their decent hands and draws through to the end. Only players who believe that making "big laydowns" is the hallmark of expert play routinely make this mistake. They are doomed to wonder why they keep losing when they play so expertly.
Another error is almost as costly. It is so common that you will see someone make it on nearly every hand of a small stakes game. The error is failing to protect strong hands in large, multiway pots.
To "protect your hand" you bet or raise. Your bet should force players who hold weak draws to decide between folding and making an unprofitable call. When you make this play, any players with weak draws who call do so to their detriment.
As a simple example, you hold
in the big blind. Two players limp, the small blind completes, and you check (4 small bets). The flop is
The small blind Checks, and you bet. If the player next to act happens to hold
your bet protects your hand. He can choose to fold his draw, as he should. If he folds, your chance to win the pot improves. You will now likely win even if a six comes.
He can also choose to call. If he does, he pays one bet to win five (the size of the pot) plus any additional bets he gains on later rounds. Since he is over a 10-to-1 underdog to catch a six on the turn, this call probably loses money. Your opponent is in a lose-lose situation. No matter what he chooses to do, he loses. Protecting your hand is the art of placing your opponents in these lose-lose situations.
Sometimes, because merely betting out will not be enough, you have to work harder to protect your hand. Assume that you hold KT in the big blind. Two players limp, and the button raises. The small blind folds. You call, as do the two limpers (8.5 small bets). The flop is again K75. You bet. The player with 98 now has a different decision. There are 9.5 bets in the pot instead of five. He is still over a 10-to-1 underdog to catch a six on the turn, but his situation is much better. If he calls and catches a six, he will almost certainly win the pot. He may also make two or three more big bets from you (plus, perhaps, some bets from other players) before you realize that you have been outdrawn. So when he completes his hand, he can expect to win the 9.5 bets in the pot plus at least four (two double-sized bets) more from you on fourth and fifth street. He is a 10-to-1 underdog to hit his card, but he will win at least thirteen bets on his one bet investment if he does get lucky. Since his call is profitable, your bet does not protect your hand.
To protect your hand here, you have to be more subtle. The player on the button raised before the flop. A player who raises before the flop will typically bet a ragged flop like this one. Many players will automatically bet with any hand; they need not have a king. You can exploit this tendency in order to protect your hand if you check, and both limpers check, the button will probably bet. Now you should raise. To see fourth street, your opponent with 98 must choose between folding and calling two bets. Since there are 11.5 bets in the pot, and it costs him two bets to see the turn, calling is again unprofitable for him. A check-raise often protects your hand when betting out does not.