Ten years ago, in a move he quickly grew to regret, Art Garfunkel had an imaginary conversation with Paul Simon while speaking to a reporter for U.K. newspaper The Telegraph. They hadn’t played together in five years at this point, and his frustrations were boiling over. “How can you walk away from this lucky place on top of the world, Paul?” Garfunkel asked. “What’s going on with you, you idiot? How could you let that go, jerk?”

The reporter asked if Simon had a Napoleonic complex, and...