"I wrote it for breakfast, recorded it for lunch and we're putting it out for dinner."

That's how John Lennon flippantly described the incredibly speedy creative process leading up to the release of his 'Instant Karma!' single -- and although it wasn't literally true, it came impressively close.

Inspired by a conversation he and Yoko Ono had with Ono's ex-husband Tony Cox and Cox's partner Melinde Kendall, Lennon arose the morning of Jan. 27, 1970, with the stirrings of a song in his head. Roughly an hour after sitting down at his piano, he emerged with 'Instant Karma!' -- and less than a month later, it was out as a single on both sides of the Atlantic.

At the time, Lennon was preoccupied with the idea of getting his music out as quickly as possible, and 'Instant Karma!' proved it was not only possible, but arguably just as effective as the meticulous level of studio craft the Beatles employed over the course of their last few albums. A huge worldwide hit, it ended up jockeying with 'Let It Be' for chart position, and ultimately ended up becoming the first single by a solo Beatle to sell a million copies. Still, even as fans sang along and lined up to buy copies, some critics couldn't help wondering what inspired the song.

"It just came to me," shrugged Lennon after David Sheff asked him how he thought of the title. "Everybody was going on about karma, especially in the '60s. But it occurred to me that karma is instant, as well as it influences your past life or your future life. There really is a reaction to what you do now. That's what people ought to be concerned about. Also, I'm fascinated by commercials and promotion as an art form. I enjoy them. So the idea of instant karma was like the idea of instant coffee: presenting something in a new form. I just liked it."

For the session, Lennon -- who was still a Beatle in the eyes of the world, even though he'd privately quit the band months before -- enlisted his former bandmate George Harrison and producer Phil Spector, as well as a roster of supporting players that included Billy Preston, bassist Klaus Voormann and drummer Alan White, who'd later go on to join Yes. For White, tracking 'Instant Karma!' would provide an early highlight in a career that ended up having more than its share.

"Even one Beatle's enough in the room, and when there's two of them the whole room kind of tends to revolve around them as people, so everybody's like, you're in awe," he marveled years later. "You're sitting in the same room, they did so much musically to change the world, basically."

Ten days after Lennon wrote 'Instant Karma!,' it was out as a single in the U.K.; two weeks later, the U.S. followed suit. It performed well on both continents, peaking at No. 5 in Britain, No. 3 in the States and No. 2 in Canada. The single was supported by an appearance from Lennon and members of his band on the BBC's 'Top of the Pops' program, ending a four-year hiatus on the show by any member of the Beatles -- and debuting a new look for Lennon and Ono, who'd recently cut their long hair and donated it to London-based activist Michael X.

'Instant Karma!' also served as a simple, powerful restatement of Lennon and Ono's message -- warning against the foolishness of "laughing in the face of love" and reminding listeners, "Better recognize your brothers / Everyone you meet / Why in the world are we here? Surely not to live in pain and fear."

By the time he and Ono returned with their next single, 'Mother,' in December 1970, their approach had changed considerably, both in terms of arrangement -- Lennon worked with a simple trio consisting of himself, Voormann and Ringo Starr -- and in terms of a far more challenging melodic and lyrical content. Over the duration of his ensuing solo career, Lennon would continue to alternate between challenging and placating fans, eventually disappearing completely between 1975-80, but with 'Instant Karma!,' he proved that even without the Beatles around, he could pen a pop anthem whenever he felt like it.

You Think You Know the Beatles?

See the Yearbook Photos of John Lennon and Other Rock Stars

More From Ultimate Classic Rock