Reply #11: It's actually from a Sci fi book

[ismnotwasm]

Cyteen by CJ Cherryh. The advice is from a villain, a mass murderer named Ariane Emory

"Brains and sex fight each other to control your life, and thank God brains get a head start before sex comes along. Sex is when you're the most vulnerable you'll ever be. Brains is when you're least. Brains have to win out, so they make a safe time for sex to happen"

And a little further;
"And for God's sake, don't ever use sex to get your own way where brains won't work. That's the dumbest thing in the world to do, because then you're operating without brains at all aren't you? That's as plain as I can make it"