If an act that I may commit carries with it a probability of .9 that I will succeed and that success will result in sufficient reward, then the fact that failure would result in death is offset. So playing Russian roulette for 1 million dollars might be tempting enough to overcome my fear of death.
So a 90% chance of becoming a millionaire might cause me to ignore the 10% likelihood that I will end up dead. If we assign a value of 1 reward point to each dollar, then 1M reward points X .9 probability of success gives me 900K reward points value for the playing the game.
But if a person is acting in a rational manner, that is, they are a rational actor, then the .1 probability of death would likely rule out my participation since for most, death would far outweigh any monetary gain that might be incurred and the value of death might be well over a billion negative points and even when multiplied by .1 would still outweigh the paltry 900K value points associated with the one million dollars after the probability of winning is calculated.
Two problems with the idea of consequences being sufficient deterrent to someone committing any specific act are that in some cases what we might assign to the successful effort is much lower than their perceived reward. And the other problem is that an actor involved in the act might terribly underestimate the probability of failure.
To those involved in an affair, or contemplating the beginning of one, the probability of getting caught and therefor actually suffering the consequences is severely underestimated. In addition, the perceived reward is of such high value to them that even a multiplier of .5 or worse for success does not become a deterrent.
These two factors combined mean that relying on consequences alone to ensure specific behavior from any group or individual can be a crap-shoot at best. As BP pointed out, the threat of death for murder seldom causes someone acting in the heat of the moment from actually pulling the trigger and ending someone else's life. This is because they have over estimated the reward and underestimated the probability of failure.
The death penalty does pretty much assure that any given person will not commit the same act twice, however, but only from the standpoint of their inability to commit the crime after they themselves are already put to death.
This is what makes the suicide bomber so difficult to deal with, BTW since for the bomber, success means death and that is at least in part their goal, to be a martyr and by dying accomplish the goal of taking others for the trip. In the case where they have been taught by religious leaders that to die in such an effort is actually the greatest of all rewards, this ensures their entry into paradise regardless of any other reward and punishment system that religion teaches or what their reward would be otherwise.
So as it applies to affairs, the reward versus consequences equation fails because of both overestimation of the reward and underestimation of the likelihood of failure or even of getting caught. Since the affair is based on emotions that are generally overwhelming to the actors, no rational consideration is even give to the process and therefor success and failure mean nothing because the feelings themselves are the reward and the lack of rational control overrides any thoughts of consequences.
So it has to be something other than consequences that act as a deterrent to future affairs and that other thing is the idea of extraordinary precautions.
A person, especially one who has already exhibited a weakness in this regard must take precautions that make a repeat affair less likely because the possible consequences alone aren't likely to result in prevention of allowing the emotions to run away once the situation begins to evolve.
Ah, but this was only an exercise that it has been too many years since performing and now it is all kind of foggy. So if you don't like the argument, ignore it, because it means didly to me anyway.
But if it's worth discussing, have fun.
With much ado about nada...