View the biography of Albrecht Dürer
But when great and ingenious artists behold their so inept performances, not undeservedly do they ridicule the blindness of such men; since sane judgment abhors nothing so much as a picture perpetrated with no technical knowledge, although with plenty of care and diligence. Now the sole reason why painters of this sort are not aware of their own error is that they have not learnt Geometry, without which no one can either be or become an absolute artist; but the blame for this should be laid upon their masters, who are themselves ignorant of this art.
And since geometry is the right foundation of all painting, I have decided to teach its rudiments and principles to all youngsters eager for art...
Welcher aber ... durch die Geometria sein Ding beweist und die gründliche Wahrheit anzeigt, dem soll alle Welt glauben. Denn da ist man gefangen.
Whoever ... proves his point and demonstrates the prime truth geometrically should be believed by all the world, for there we are captured