Like most of the early Fleetwood Mac songs, this was written by Peter Green. It is a very sad song, a real cry from the heart. At the time of writing this Peter Green was struggling with the band's success, and his increasing fortune. His instabilities had been bought to a head by a three day LSD binge.
Mick Fleetwood recalled that "Man Of The World" was "like saying 'please help me'" and Peter Green's leaving the band was "the most threatening thing that I can relate to in the ranks of Fleetwood Mac."
In 1996, Mojo magazine tracked down Peter Green, who retained most of his memories from the '60s before started taking LSD. Regarding this song, Green quipped: "The lyrics are corny, hammy. Shall I tell you about my life?... My life! That's Jewish for a start, isn't it?!" (Green was raised Jewish)
Peter Green quit Fleetwood Mac a year after this was released and gave all his money away to charity. He played a few gigs with the band in 1971, but once again vanished. In 1977, when it seemed he was again interested in performing, Mick Fleetwood arranged a record deal for Green, but it fell through when Peter refused to sign the contract.
Reflecting back on the song in 2015, Mick Fleetwood told Mojo: "It's a sad song. Had we known what Peter was saying... What's that line? 'How I wish that I'd never been born.' You know, whoa. It's pregnant with passion, it's a prayer, it's a crying out."