"Be eager to lend a patient ear to the opinions of others and think long and hard whether whoever finds fault has reason or not to censure you. And if the answer is yes, correct the fault. If no, give the impression that you have not heard him, or if he is a man whom you respect, explain to him why he is mistaken."
"There is nothing that deceives us more than our own judgement when used to give an opinion on our own works. It is sound in judging the work of our enemies but not that of our friends, for hate and love are two of the most powerfully motivating factors found among living things."
"Shadows which you see with difficulty, and whose boundaries you cannot define ... these you should not represent as finished or sharply defined, for the result would be that your work would seem wooden."
"He who draws ... ought to take his position so that the eye of the figure he is drawing is on a level with his own ... because generally figures or people whom you meet in the streets all have their eyes at the same level as yours, and if you make them higher or lower you will find that your portrait will not resemble them."
"He who despises painting has no love for the philosophy in nature."
Leonardo da Vinci.