Paul, on writing "I'm Looking Through You", and on songwriting as a way of dealing with emotional baggage:
"[Jane] went down to the Bristol Old Vic quite a lot around this time. Suffice it to say that this [song] was probably related to that romantic episode and I was seeing through her facade. And realising that it wasn't quite all that it seemed. I would write it out in a song and then I've got rid of the emotion. I don't hold grudges so that gets rid of that little bit of emotional baggage." (Paul McCartney, Many Years from Now, p. 276)
Good advice from the guy whose default demeanor is wink-and-thumbs-up. Don't sit around with a grudge. Do something creative with it. Write a song, write a poem, draw a picture, turn it into a short story, journal it - hell, get out a couple of cans of Play-Doh and make a throwaway sculpture. Anything is better than burying the baggage and letting it ferment.
Listen to what the man said.