Few things are more gratifying that finishing something that looked impossible at the beggining. Da Vinci always thought he was mistaken at most of the things he accomplished, and he continued hard working pursuing perfection. Now we know he was wrong most of the times, but if he thought he did it perfectly, we cannot feel the pleasure to delight us with his phenomenal works today. That is the way progress is built on.
Fantastic post, by the way!