Sincerity
It is not enough that the painter should make the spectator feel what he meant him to feel; he must also make him feel that this feeling was shared by the painter himself bona fide and without affectation. Of all the lies a painter can tell the worst is saying that he likes what he does not like. But the poor wretch seldom knows himself; for the art of knowing what gives him pleasure has been so neglected that it has been lost to all but a very few. The old Italians knew well enough what they liked and were as children in saying it.