Matthew O’Brien, writing for The Atlantic about the interesting history of engagement rings:
Put simply, if the man didn’t fulfill his obligation to marry, the woman had legal recourse. This calculus changed once the law changed. Suddenly, women wanted an upfront financial assurance from their men. Basically, collateral. That way, if the couple never made it down the aisle, she’d at least be left with something. And that something was almost always small and shiny. The diamond ring was insurance.
I feel like there is a joke here about premiums and quality of coverage, but I’m too tired to think of one.