[StellarWind]

The (expected) value of a hand is the amount of money you will make off the hand averaged over all possible outcomes. This is how much money you should receive if someone walks up and offers to buy your hand at some point during the play.

A very important property of hand value is that it can never be negative. You always have the option of folding and folding has value zero.

The expected value of a preflop call is the average value of the hand after all possible flops. This will include great flops that have a lot of value and terrible flops that have almost no value. There is no such thing as a flop that has negative value. Actually flops cannot have zero value either because it's possible that no one will ever bet and you will eventually win at showdown without risking any money. But many flops are bad enough that they can be considered zero for practical preflop purposes.

A preflop call is +EV if the expected value of the call is greater than the cost of calling. I've neglected the possibility of further preflop raises, possible overcalls and overfolds behind you, and also the possibility that raising yourself might be an even better play, but if you understand the concepts you should be able to adjust for these issues.

Now it may happen (e.g. AK vs QQ analysis) that there are many bad flops where checkfolding has zero EV but chasing is better because it has a miniscule EV of say +0.05 BB. That means chasing is correct. It also means that you will frequently lose a lot of money on the hand and your variance will increase. But from a preflop perspective it's still one possible flop that might be +0.05 BB or just plain zero. The effect on your preflop EV is utterly insignificant.

This whole idea you read of bad preflop actions sucking in money through the whole hand is just a myth perpetrated by the mathematically ignorant. No one is forcing you to make negative EV plays postflop.

Hmmm, that was harsh. A more understanding statement would be that it reflects the reality that for inexperienced or weak players certain hands do have a trapping effect. These players make serious mistakes chasing unplayable flops and lose money postflop. What the authors really mean is that a beginner should fold marginal hands that are profitable for good players because they will be unprofitable for the beginner.

So actually a flop could have negative EV in the sense that although folding is the correct play, Hero is not good enough to make that play. But I would never compute the EV of a preflop play based on the assumption that a particular flop had negative EV, because if I thought that then I would realize that I should fold that flop and my EV would stop being negative.