The man who knows only one subject is almost as tiresome as the man who knows no subject.
Source: In Quotable Business, ed. Louis E. Boone, 1992.
-- Charles Dickens, (Feb 7 1812-1870), English novelist, dramatist; He was one of most prolific and popular English novelists, e.g., A Christmas Carol, 1843 & Tale of Two Cities, 1859.