Nothing can be soundly understood
If daylight itself needs proof.
Imām al-Ḥaddād (trans. Moṣṭafā al-Badawī), "The Sublime Treasures: Answers to Sufi Questions"
Reminds me of Moore's "here is a hand" paradox (or one man's modus tollens is another's modus ponens).
Here's the new thread for posting quotes, with the usual rules: