Some deep thought on "the principle of reason" can be found in Heidegger's essay The Essence of Ground in Pathmarks.
Quoting from the start and the end to give a flavour of the content.
The Problem of Ground
The "principle of reason" as a "supreme principle" seems to preclude
from the very outset anything like a ...
The term 'rational' is related to the term 'ratio', and implies the ability to effectively measure and balance concepts and ideas. It's a natural analogy to applying principles of geometry to crafts. A man who doesn't measure or calculate well is a sloppy craftsman, and builds (say) weak, wobbly, oddly-proportioned furniture. A man who does measure and ...