The Preselection Effect is when one woman becomes more interested in a man, simply because other women are interested in him. The rationale being that if he pulled all their interest, he must be something special.
So when other women start expressing interest in you, your wife tends to sit up and take notice. Not merely for the imagined threat of you sleeping with them or dumping her for one of them, but simply because other women are interested in you.
So part of the reason I advise men to self-improve and become more attractive, is not to just directly pull their wife’s interest better, but to also pull the interest of other women. Thus creating a preselection effect.
The key though, it that it’s preselection when another woman is interested in you, as opposed to you hitting on another woman.