I found this quotation from Piatigorsky in Dorothy Lamb Crawford's A Windfall of Musicians:
"You don't have to be a genius to know your shortcomings, because there are so many of them. But you have to be a mighty intelligent person to know your strong points. That is your obligation: to know what is good. And if possible to enjoy. And everything that you don't like, to convert into something that is likable. That is the only way I know. Otherwise you will live in the negative all your life. You can't live in that, you can't prosper in it. . . . I never met a really, truly conceited musician. Because they know what they don't know--especially before a concert. . . . Music remains above you. The better you become at it, the music moves higher, so it becomes unreachable."