[Zybomb]

It's basic math.

If X= Opponents Stack (we'll say $1000)

Y= % of time we'll stack him (we'll estimate this by 1) his likely holdings and 2) how he'll react with them. For example if you know your opponent ONLY raises with large pairs and will put his entire stack in with an overpair each time, (extreme example) this would be 100%. More reasonably, let's say 25% for this example

and Z= the amount we must call (i.e his preflop raise)

We take X (1000) times Y (25% = 250 and that must be greater than 8*Z. We get 8 because we will flop a set roughly 1 in 8 times (we will hit a set one out of 5 times yes, but that assumes we will see the turn and river as well)

So say the blinds are $5/$10 and his raise is to $40 we'd take $40*8 and get $320. Assuming our stack % of 25% is accurate then we should fold this hand bc it is -EV (we win $250 when we hit a set ... yes i realize we win 1000 if we stack our opponent, but we only do so 25% of the time so hitting a set has an EV of 250) Yet we need to call $40 8 times (320). Is the % 25% always? Of course not. It could be as low as 5% (complete rock) or as high as 100% (extreme example given above)

Of course this is basic. I would still call with my pair bc this formula doesnt take into consideration

1) other players (and thus more $) in the pot
2) the possibility of being paid off our villains entire stack plus additional money from other players
3) the times we win the pot without hitting a set

Hope this explains a little bit