The irony is that the most responsible thing for married couples to do when considering permanent birth control is talk openly about the impermanence of their union.
The first time my boyfriend and I had sex, of course we used a condom. Even though I had just met him, and have an amazing eight-year-old daughter, I had second baby cravings, and they were strong.
A federally funded study of newlyweds asked them to rate their chances of ever divorcing on a 0-10 scale.
The psychology part is that we want to believe we have made good choices about really important things, and we tend to ignore evidence to the contrary.
Since marriage is supposed to be once and for life, believing that your marriage is at risk for splitting up is an admission that you messed up in a central life decision.
This explains the oft reported research finding that the vast majority of married couples say they are above average in marital satisfaction, even couples who then divorce within a few years.
We need to believe in our marriage as long as we can, because so much is at stake.
And they may be more attached to just being married than women are; women often have higher expectations for the quality of the marriage and move on when they give up hope for that quality.