After my first year of marriage, I suggested that the best place to hide jewels would be in the back of the refrigerator since most thieves are men, and men can never find anything in the back of the refrigerator. Raising three sons confirms that it's testosterone-induced blindness.
This is not to disparage the stronger sex. Married men tend to earn more money than single men -- as much as 44 percent more after controlling for age, IQ, education, experience, race and number of children. Economists call it the marriage premium.
Speculation as to the provenance of this bounty includes "ability bias," i.e., those men who are able to earn more money are better able to attract spouses; "signaling," meaning that being married signals reliability and other valuable traits to employers; and "human capital," i.e., being married makes men work harder, curb their tempers, and otherwise perform better at work.
I lean to the human capital explanation. Brain research has shown that, on average, women are better at understanding emotions than men. Married men have advantage over their single co-workers, in that they can consult their wives regarding interpersonal conflicts and questions. Their wives can help them to understand what's really going on. My mother performed this function for my dad for years.
This is only part of the explanation (which is pure speculation I freely admit). By itself, this feminine psychological insight would suggest that women should earn more than men, and that isn't the case. No, the other piece of the puzzle regarding married men and work is love and appreciation. Married men work harder because they know they are working for the welfare of those they love. Married women probably convey their gratitude to their husbands for providing the security they and the children need, and this cements a man's place in the world.
The "marriage premium" doesn't work for cohabitating men, nor for those who father children they don't raise. The "piece of paper" matters. Something to consider the next time someone celebrates the decline of "traditional" marriage.