Was he smart? No, not exceptionally. Instead, he was a genius. - Walter Isaacson

he never finished any of the works he began because, so sublime was his idea of art, he saw faults even in the things that to others seemed miracles.

Those who are in love with practice without theoretical knowledge are like the sailor who goes onto a ship without rudder or compass and who never can be certain whither he is going,” he wrote in 1510. “Practice must always be founded on sound theory.”11

Knowing that great conceptions are worth little without precision execution