“As you grow older, you'll find the only things
you regret are the things you didn't do.”

- Zachary Scott
(24 Feb 1914 - 03 Oct 1965)

The song is an example of Lennon–McCartney collaboration^[4] at a depth that happened only rarely after they wrote the hit singles of 1963. This song, "A Day in the Life", "Baby, You're a Rich Man" and "I've Got a Feeling", are among the notable exceptions.^[3]

McCartney wrote the words and music to the verses and the chorus, with lyrics that "might have been personal", probably a reference to his relationship with Jane Asher.^[5] McCartney then took the song to Lennon:

"I took it to John to finish it off, and we wrote the middle together. Which is nice: 'Life is very short. There's no time for fussing and fighting, my friend.' Then it was George Harrison's idea to put the middle into waltz time, like a German waltz. That came on the session, it was one of the cases of the arrangement being done on the session."^[5]

With its intimations of mortality, Lennon's contribution to the twelve-bar bridge contrasts typically with what Lennon saw as McCartney's cajoling optimism^[6], a contrast also seen in other collaborations by the pair, such as "Getting Better" and "I've Got a Feeling". As Lennon told Playboy in 1980:

"In We Can Work It Out, Paul did the first half, I did the middle eight. But you've got Paul writing, 'We can work it out / We can work it out'—real optimistic, y'know, and me, impatient: 'Life is very short, and there's no time / For fussing and fighting, my friend.'"^[7]

Based on those comments, some critics overemphasised McCartney's optimism, neglecting the toughness in passages written by McCartney,^[6] such as "Do I have to keep on talking until I can't go on?". Lennon's middle shifts focus from McCartney's concrete reality to a philosophical perspective in B minor, illustrating this with the waltz-time section suggested by George Harrison that leads back to the verse,^[5] possibly meant to suggest tiresome struggle.^[6]

Music critic Ian MacDonald, said:

"[Lennon's] passages are so suited to his Salvation Army harmonium that it's hard to imagine them not being composed on it. The swell-pedal crescendos he adds to the verses are, on the other hand, textural washes added in the studio, the first of their kind on a Beatles record and signposts to the enriched sound-palette of Revolver."^[6]

The Beatles recorded "We Can Work It Out" on 20 October 1965, four days after its accompanying single track, with an overdub session on 29 October.^[8] They spent nearly 11 hours on the song, by far the longest expenditure of studio time up to that point...^[6]