A memorandum is written not to inform the reader but to protect the writer.

Dean Acheson (1893-1971) American statesman

“Acheson’s Rule of Bureaucracy”
    (Source)

Quoted in Alan Otten, "Politics and People: More Rules," Wall Street Journal (1977-09-08). Paul Dickson's The Official Rules (1978), indicates that it was recalled by Harold P. Smith for Otten.