Full Idea
I am assuming the following principle: Clutter Avoidance - in reasoning, one should not clutter one's mind with trivialities.
Gist of Idea
It is a principle of reasoning not to clutter your mind with trivialities
Source
Gilbert Harman (Change in View: Principles of Reasoning [1986], 2)
Book Reference
Harman,Gilbert: 'Change in View: Principles of Reasoning' [MIP 1986], p.12
A Reaction
I like Harman's interest in the psychology of reasoning. In the world of Frege, it is taboo to talk about psychology.