After nine years writing Slate’s “Dear Prudence” advice column, Emily Yoffe has noticed some recurring themes: “Mothers in law, husbands addicted to porn, impossible officemates, crazy brides.” Sometimes, Yoffe says, letter-writers say they’re prepared to abide by her advice, whatever it is. “I have people writing to me, saying ‘I thought we wanted three children, but I realized I’m happy with two.