Nick Laird-Clowes, was one of the luckiest dudes in R'n'R history. The story goes thata friend of his (girfriend I think) was acquainted with Paull Simon, iirc because she lived down the hall from the flat Simon kept in London at that time. Anyway, he got to hang out with Simon on evening, just plinking around on the guitar, and he told Simon that he had just come up with this riff: "hey-oh ma ma ma".
Simon liked it a lot (not surprising considering how many of his songs have that kind of stuff in them (c.f. "The Boxer", et al.).
Next thing you know, he had a band, a contract & David Gilmour producing. The completed song was supposedly an elegy for Nick Drake.