Whoever came up with the phrase “if I called the turn and nothing changes I have to call the river” is not experienced in big bet poker. In fact, you can make some very tough folds on the river because you called a big bet on the turn. Most opponents, especially at the lower levels, are incapable of three barrel bluffing or value betting thin when the pot is large. Because of this we can often come to the conclusion that if our opponent bets big on the river after we call the turn he has a strong hand.
Let us take an example—With effective stacks of $700 we raise from under-the-gun to $20 with A ♦ A ♣ in a $2-$5 no-limit game and get two callers. The board comes out J ♣ 5 ♦ 2 ♠. We bet $40 into $60 and the big blind check-raises us to $140. We call. Turn is the 6 ♥. The big blind bets out $200 and we call. River is the T ♠. The big blind moves all in for $360. The T on the river here is a pretty inconsequential card. Most likely if we are beat we were beat before the river. Why do we call the turn then? The answer is simple—to evaluate if we have the best hand and so that we can safely fold the river. Our turn call looks so strong and because we appear to be getting decent pot odds on the river we gain information about the strength of our opponents hand by the shear fact that he has bet once again—especially if it is all-in.
We can use the same technique if we are playing a hand from out of position. Most low-level players love to go to showdown on the river with their medium strength hands especially as the pot gets big. Let us say we were out of position in the above example. We bet $40 first to act and are raised to $140 on the flop. We call. Our opponent keeps the pressure on us and we check call $200 on the turn. On the river we once again check, and our opponent checks back AJ. You see this type of play all of the time. Lower level players get scared when the pot gets big and are frightened that they may get raised off of their hand when they bet the river. For this reason they often go to showdown with hands that are worth value-betting. Because we have this information we can safely check fold a lot of rivers because we know that this type of opponent will only bet his monster hands and check back all of the holdings that we beat.