Where did John Lennon Get The Idea to write Dear Prudence?

Where did John Lennon Get The Idea to write Dear Prudence?
MIA FARROW TALKS BEATLES with LETTERMAN 1994
Hear Dear Prudence @ https://youtu.be/wQA59IkCF5I
John Lennon's original skeletal version of 'Dear Prudence'
https://youtu.be/OKUgZ7foKuw
Meet Prudence:
Dear Prudence- An Interview With Prudence Farrow Bruns
https://youtu.be/jC_V-oCTceQ

Видео Where did John Lennon Get The Idea to write Dear Prudence? канала Tony DeSanto