Full Idea
The discovery that 1 is a number must have been difficult.
Gist of Idea
Discovering that 1 is a number was difficult
Source
Bertrand Russell (Introduction to Mathematical Philosophy [1919], I)
Book Reference
Russell,Bertrand: 'Introduction to Mathematical Philosophy' [George Allen and Unwin 1975], p.3
A Reaction
Interesting that he calls it a 'discovery'. I am tempted to call it a 'decision'.