An historian is an unsuccessful novelist.
H. L. Mencken (1880-1956) American writer and journalist [Henry Lewis Mencken]
A Little Book in C Major, ch. 7, § 21 (1916)
(Source)
Variants:
HISTORIAN. An unsuccessful novelist.
[A Book of Burlesques, "The Jazz Webster" (1924)]
Historian - An unsuccessful novelist.
[Chrestomathy, ch. 30 "Sententiae" (1949)]