About the ancient Greeks:
Logic was the rage of the day; all over, at the marketplaces, in the streets, in private homes and in public buildings, at all times, sometimes all through the night, people engaged in dialectical disputations and flocked to hear the acknowledged masters of logical argument display their art. The writings of this period mirror this development in thought: drama as well as the dialogue bear witness to the power which the newborn science wielded over the imagination of men1.
About Renaissance painters:
It was said of Uccello that the discovery of perspective had so impressed him that he spent nights and days drawing objects in foreshortening, and setting himself ever new problems. His fellow artists used to tell that he was so engrossed in these studies that he would hardly look up when his wife called him to go to bed, and would exclaim: 'What a sweet thing perspective is.'2
No grand moral here, but I think it's interesting how intellectual enthusiasms burn so brightly in the beginning. (I should add some quotes about enthusiasms that burned brightly and then burned out, leaving nothing but wasted nights and broken marriages.)