"You don't need an argument for buying butter. It's a natural, human instinct."
(Context: Lord Peter, undercover at an advertising agency, is first put on a margarine account. Why, he wonders, would anyone pay more for butter when, as he is instructed to put in his copy, margarine is just as good for a fraction of the cost. If that's the case, "what's the argument for buying butter?" He is told the above as a response.)
(Larger context: A few weeks ago at a gathering of colleagues, Dorothy L. Sayers came up, as a number of us professed our love of her. And since then, I've been doing a little re-reading. I can't read the hard stuff, the Harriet Vane novels, because I've lent them out to someone else [who gained a desire to go back to the novels at the same gathering]. But after trifling with one of the early ones, I've since moved on to the fantastic Murder Must Advertise, which is fantastic not only because of the goings-on at the ad agency, but also because it's the only thing I've ever read that made me feel like I might have a sense of how cricket works.)