I found Art & Fear: Observations On the Perils (and Rewards) of Artmaking by David Bayles and Ted Orland by way of a British blog, The Beatles Songwriting Academy, devoted to learning to write songs by studying the Liverpool lads. It’s not just a worshipful fan site: blogmaster Matt Blick rebukes them for lame songs (his “Hall of Shame” includes “Maxwell’s Silver Hammer”) and for some stinky rhymes that mar great songs. But Blick has a “Be-atltudes” page, too, in which he enumerates virtues, especially the prolificacy of Paul McCartney and John Lennon:
“Between 1962 and 1970 Lennon & McCartney wrote close to 200 songs. Almost all were recorded and released. The majority were top 10 hits as singles or album tracks. Whereas most writers today would throw away a song that wasn’t good enough for their next album or didn’t fit stylistically, the boys always had a reason to finish that song. And because of their insane recording schedule they always had to come up with more songs.”
Mates and rivals, who happened also to be gifted, Lennon and McCartney inspired and goaded each other to craft new work. What’s ranked as one of the greatest songs ever written, and their masterpiece, “A Day in the Life,” which concludes Sgt. Pepper’s Lonely Hearts Club Band, showcases their separate gifts being expressed together under the pressure to come up another tune. They melded utterly separate lyrical fragments each had written.