In this case, the song in question is still a treasured piece of virtually every stage production of The Music Man, but was left out of the famous film version. It’s a very serious, almost severe song with an almost aria-like construction, and it perfectly sums up Marian’s character, telling us exactly who she is and what she wants without ever seeming expository or heavy-handed for a moment. There’s no clear explanation for why it didn’t make it into the film, but there is a fairly obvious theory. There were persistent rumors for many years that this song was ghostwritten, as a kind of gift, by Meredith Wilson’s friend and colleague Frank Loesser, and those rumors have now essentially been confirmed: there are recordings available of the two pieces of music from The Most Happy Fella…a cut song and a bit of underscoring…that, when combined, form the tune of “My White Knight”. Loesser never attempted to claim credit for the song, so it seems unlikely that Wilson was forced to drop it from the film, but the most plausible explanation is that Wilson simply didn’t feel comfortable using a number written by someone else in the film for some reason. The problem is that the song it was replaced with, “Being In Love”, while certainly pretty, is entirely incorrect for Marian’s character, and its bubbly, upbeat sound clashes with the earnest tone of the original number’s recitative-like middle section, which was retained. Despite not being at all a bad song in its own right, the inclusion of “Being In Love” is the only major flaw in an otherwise near-perfect film adaptation, and you could argue “My White Knight” constitutes the primary incentive to actually see the show in the theater, given the quality of most revival versions.