Understanding Marginal Situations
In poker, some situations are very hard to judge. Call or fold - it seems like such a close decision that you cannot really tell them apart. It's a marginal situation.
For natural reasons this is the kind of situation we talk about the most. We can spend hours or even days going over them and wondering if we should have folded instead of calling, or called instead of folding.
This is kind of funny, because the very definition of marginal situations tells us that they aren't very interesting.
Call or fold comes to the same
Whether we fold or call in these situations, we'll have the same amount of money in the poker account in the end of the year. Our expectation is the same in both cases.
For example, let's say there's $100 in the pot on the turn. Your opponent moves in with his last $100. For some reason you know that your chances of winning if you call are exactly 33%.
In this situation your expectation (EV) if you call is exactly zero: one time out of three you win $200 and two times you lose $100. If you fold, the expectation is zero as well, for obvious reasons.
Focus on something that matters
This is a truly marginal situation, and as long as we look at your expected profit, it doesn't matter what you choose to do.
Just fold or call and move on to the next hand. Weighing down your friends' moods with eternal discussions of this unimportant decision is pointless.
On the other hand, by calling or folding you choose your level of variance. If you call, your swings will be greater than if you fold. Things outside of the current hand may advise you to maximize or minimize variance.
How big swings do you want?
As an example, if you're taking a shot in a high stakes game, you may want to play high variance. Double up or go home. In that case you would insta-call here.
Or if you're short stacked in a tournament, you may reason that a small stack isn't much better than no stack at all. You may choose to call to give yourself a bigger chance to approach the other stacks and get some equity.
If you're in a satellite where all paid places are equal in value, you'd typically want to minimize variance in marginal situations. Or if you're a grinder trying to steadily build a bankroll.
Speaking of bankrolls - the smaller swings you have, the lower are your bankroll requirements. Their very purpose is to keep winning players from going broke due to variation.
Put in another way, the more low-variance decisions you make, the higher stakes you can play with a certain bankroll.
For many players, smaller swings are preferable from a psychological perspective, since big losses tend to get at them and maybe even make them play worse. Others again seem to thrive when things go really wild. It's a matter of style.
From the viewpoint of game theory
From a game theoretic perspective, marginal situations actually define optimal play. To be more clear-cut: if your actions give your opponent a marginal situation, you're playing optimal poker.
That is, optimal in a game-theoretic way. As you know, this doesn't mean it's your best way of action. Playing optimally prevents others from taking advantage of your play, but it also prevents you from taking advantage of theirs.
