Full Idea
Real human beings are not, for the most part, in conscious control of - or even consciously aware of - their reasoning.
Gist of Idea
We are largely unaware of how we reason
Source
G Lakoff / M Johnson (Philosophy in the Flesh [1999], 01)
A Reaction
The accceptance of this idea sweeps away huge chunks of the philosophical tradition, but it strikes me as correct. Most people hold lots of strong views, but struggle to articulate why they hold them.
Book Reference
Lakoff,G/Johnson,M: 'Philosophy in the Flesh' [Basic Books 1999], p.5