The HEY JUDE star was considering turning his back on his illustrious career - but the response of people affected by the terrorist attacks to his music made McCartney realise he still has much to offer the world.
He says, "9/11 was really the beginning of it all. Before that I was wondering if I wanted to tour again, dabbling a bit, then 9/11 happened.
"It reawakened something in me. In one way it led to everything that has happened since, the tour of America, Live 8, all that."