A person who publishes a book wilfully appears before the populace with his pants down.

Edna St. Vincent Millay (1892-1950) American poet

Letter (1927-05-25) to Cora B. Millay
    (Source)

Letter to her mother trying to calm Cora's nerves about sister Kathleen's impending first book of poetry. The letter is collected in Letters of Edna St. Vincent Millay (1952) [ed. Allan Ross MacDougall].

This passage is almost universally misquoted as "A person who publishes a book wilfully appears before the public with his pants down" (italics mine).

Another variant appears here. It shortens the first sentence, and then pulls in (and re-genders) two sentences from later in the letter:

A writer appears before the public with his pants down. If it is a good book, nothing can hurt him. If it is a bad book, nothing can help him.