Full Idea
Wittgenstein remarked that if you tried to doubt everything, you would not get as far as doubting anything.
Gist of Idea
Total doubt can't even get started
Source
report of Ludwig Wittgenstein (On Certainty [1951]) by Michael Williams - Problems of Knowledge Ch.14
Book Reference
Williams,Michael: 'Problems of Knowledge' [OUP 2001], p.159