Paul McCartney cannot read or write sheet music

However, he is completely unable to read or write a note of sheet music.

He just never learned. Why would he need to?

Funnily enough, McCartney wrote a symphony a few years back-- it was called Standing Stone-- but because he could not write or understand sheet music, he had to compose the symphony with a computer program: He literally had a system rigged up where he could compose by playing into a keyboard set up with a computer that would transcribe the music he played into sheet music, then let him tweak it.

Still, just think: if someone so good can get by wholly without knowing to read or write sheet music, then that gives so much hope for the rest of us.. because it means all you have to do is excel at what you want to do, and the conventionally "necessary" skills aren't..

Similarly, on his earlier orchestral work Liverpool Oratorio, McCartney had the help of Carl Davis, and on the Beatles' records George Martin orchestrated.

In other words, McCartney lacks a vital skill he needs to realise his work. Luckily, he is good enough that people are willing to do this grunt work for him, but most people aren't Paul McCartney.

Having a working knowledge of the tools of one's trade is never a handicap, and the fact that it is possible for a genius to create good work without the use of those tools does not mean they couldn't have created even better work if they knew them. Nor does it mean an average-to-good craftsman could do the same if they didn't have the required technical knowledge.