Follow the controlled scream of Sir Paul's younger voice (which out-Little Richards Little Richard's) and his loopy bass guitar through this thing: they start out urgently and by the end of the song, they've made you understand the wretchedness of being loved less than you love. And because you've had no choice but to sing along, there's nothing vicarious about it: screaming in agony is hard and exhausting work (especially when you've lost the will for almost everything else).
Guess what? You've just been beaten up by a gazillionaire choir boy who, because he somehow knows what it's like to nearly break down and die, understands you better than anyone else. This song hurts.