India, Jan. 23 -- Ah, old movie tropes! Cops would get into NYC taxis and yell, "Follow that car!". Dudes, giving CPR to total strangers would yell "Don't you die on me!" Young women had glamorous jobs at fashion magazines (Kate Hudson literally only did one How To article a month in How To Lose A Guy in 10 Days). And amid it all, that curious little rom-com fantasy: The fallback marriage pact. Two friends would promise each other that if they are both still single by a certain age, they'll marry each other.

Screenwriters loved this Plan B cliche. "Back then, it was practically a 90s-2010s rom-com rite of passage," says Kalpak N. B., 37, author and creator of Character Biopsies on Instagram. Monica and Chandler did it in an early season ...