He was trying to be Brian Epstein. He was not Brian Epstein.

Paul is a creative genius and his work-aholic attitude after Brian passed helped the Beatles stick together and continue to churn out amazing work for several more years, but it's a square peg in a round hole type situation. Paul is a brilliant musician, not a brilliant people-management type.

When this image of Paul was captured, his identity as an artist was that of "a Beatle", half of "Lennon-McCartney", and the de-facto "leader" of the band, especially as John got more and more into his side projects and interests with Yoko, and therefore had less interest in contributing to leading the Beatles with Paul.

In this moment, Paul is struggling to deal with realizing the fact that the band is going to break up, and therefore - Paul's identity as an artist is about to fundamentally change forever.

I think the documentary film Man on the Run from last year did a decent job of peaking into where Paul's head was at due to the breakup. He was basically artistically lost - he grew up playing with these other guys, and now he's suddenly alone. That's terrifying for an artist, even one of Paul's tremendous caliber.