This is my all-time favorite quotation about
one-letter words, probably because it encapsulates the concept of the microcosm:
I was the only adult in the world who knew that ... a single letter of the alphabet would suffice for the entire encyclopedia. —Sandi Kahn Shelton, Sleeping Through the Night and Other Lies
The illustration of the letter "I" is by
Tauba Auerbach, whose alphanumeric work is endlessly fascinating.