where ideas come from

I took the excerpt below from this excellent article in The Independent, "Why don't we make good ads anymore?".
They interviewed the likes of Sir Martin Sorrell, Trevor Beattie, John Hegarty, and others, who offered their insight about the industry.
But the excerpt I took is from Sir Frank Lowe, a little bit out of context, but it offers a glimpse on how some of the world's greatest ads were created (by somebody who must know).
"...How many hours did it take Terry Lovelock to write "Heineken refreshes the parts other beers cannot reach"? He wrote it in the middle of the night in the La Mamounia hotel in Marrakech. He woke up and wrote it by the bedside. "Happiness is a cigar called Hamlet" was written by Tim Warriner when he lit up a cigar on the top deck of a London bus. How many hours was that? I found Stella Artois's "Reassuringly expensive" in the body copy of a print ad written by Geoff Seymour. It wasn't written as a line. "Every little helps" for Tesco was written by Paul Weinberger between going in and out of the loo when we were having a drink at the Paxton's Head pub in Knightsbridge." (via 407 In Vitro)