The rule of thirds holds for a lot of traits. Here, DaVinci applies it to enlightenment. Da Vinci was a genius in the truest sense of the word. Everything that he has said or has created should be carefully examined in order to gain maximal insight. Hippocrates may have been the first to use the rule of thirds in his well-known insight regarding health and wellness: 1/3 of patients get better on their own; of those remaining, half will benefit from treatment while half will be treatment resistant.