Leonard Woolf (1880-1969), Beginning Again: An Autobiography of the Years 1911 to 1918
(London: Hogarth Press, 1964; rpt. 1972), p. 185:
I have often irritated people by saying that an intelligent
person can become what is called an 'authority' on most
'questions', 'problems', or 'subjects' by intensive study for
two or three months. They thought me arrogant for saying
so, or, if not arrogant, not serious. But it is true. The number and volume of relevant facts on any subject are not many or great and the number of good books on it are few. If you have a nose for relevant facts and the trails which lead to them—this is essential and half the battle—and if you know how to work with the laborious pertinacity of the mole and beaver, you can acquire in a few months all the knowledge necessary for a thorough understanding of the subject.