“I’m very sorry,” the drone said, without a trace of contrition. - Iain Banks

One should never regret one's excesses, only one's failures of nerve.

“Let’s waste a little time, hmm?”
“A nice euphemism, sir,” she mused distantly. He smiled. “Come and help me think of better ones.” She smiled and they both looked at each other. There was a long pause.

It gripped her hand gently. 'Regret is for humans,' it said.
She laughed. 'Really?'
The machine shrugged and let go of her hand. 'Oh, no. It's just something we tell ourselves.