"It's biological."

"'I have an idea,' I say. 'Since you're attracted to me and I'm attracted to you, why don't we go to my house and have sex and see what happens next, no strings attached?'

'That would be a betrayal of Marc.'

'You could call it that, or you could call it adding another gradation into the field of your trustworthiness.'

'Having sex with you would turn me from being trustworthy into being untrustworthy.'

'Not necessarily' I say. 'If we sleep together once and it's not incredible, you'll be more trustworthy and committed to Marc from that point on, because when you see my muscles through my T-shirt and feel attracted to me, you'll think, I've already had sex with Lincoln and it wasn't that great, so who cares about those muscles?'

'You're cloaking your lust in logic.'

'My lust is logical.'

'Lust is never logical," she says. "It's biological.'"

-- Jennifer Egan, The Candy House