In a vacuum

The phrase "in a vacuum" is used to explain making decisions in a poker hand. It refers to decisions that are optimal in one particular hand (say, if it was the one and only hand you will ever play) versus the description of plausible outcomes over the course of a larger sample (What decision or strategy produces the most return over the course of playing a situation say, 1000 times). It's a very simple concept, but is hard to think about in in these terms, probably due to our short-term attachment to winning every hand that we play, as opposed to thinking in terms of which strategy earns the most return in the long run. I'd like the advice of someone that is experienced with this concept that can articulate it and perhaps give a few examples. Any thoughts are welcome and appreciated.

Well, lots of people treat opening ATC from the BTN as if preflop were a vacuum because they "believe" that the dead money earned when the blinds fold will easily compensate for doing so. If it was +EV (and I'm not saying it isnt!) whats the difference between opening K2s or 73o vs opening KK... (in "a vacuum")?

Basically the "in a vacuum" Idea is where you should start when deciding what play to use in common situations. You are calculating expected value. It is actually pretty simple. (do this away from the table, with real factual numbers whenever possible):

(outcome A * % it will happen) + (outcome B * % it will happen) = Expected Value.


A simple example is light 3-betting. In this case your opponent is opening from the hijack position for 3bb, and folding to 3-bets ~90% of the time. If he does not fold, he 4 bet shoves all in. You fold 100 % if he shoves because this is a bluff. In theory, if you raise him 3x, you win money every time you raise him EVEN WHEN YOU GET 4-BET and have to fold. Here is how it breaks down:

((3bb raise +1.5bb in the blinds)*.9) + (-9bb raise *.1)
= 4.05 + -.9
= +3.15 bb on average every time you make this play.

This is a starting point. Sometimes you have to make a different play.