From Tom Koch's obituary:
“People would say I must have had such a great life doing this,” Mr. Koch once recalled, “people who were engineers, doctors, insurance salesmen or whatever. But it was the kind of work where every morning I would wake up and think, ‘My God, I wonder if I can do it again today.’ There is no way you prepare to do it, or even know how you do it.”
In a similar vein, this from Ian Svenonius:
If one becomes a lawyer, scholar, mechanist, typist, scientist, production assistant, or what-have-you, the world will commend your decision. Each day at lunch, on vacation, or at whatever party you attend, your choice will be applauded, upheld, and affirmed. And you will know what is expected of you. Even if your job is difficult—if you are a brain chemist, international death merchant, or rocket designer—your responsibilities will be obvious and your goals concrete. If you achieve them, you may be rewarded by promotion. If you fail, you might be fired or demoted, but nonetheless—unless your boss is insane—the job will have tangible parameters.
[Art], however, is different. You will never know exactly what you must do, it will never be enough… no matter what change you achieve, you will most likely see no dividend from it. And even after you have achieved greatness, the infinitesimal cadre who even noticed will ask, “What next?”
Yes indeed. Reminds me of how my late husband used to prod me if a quilt came back from a competition with a ribbon. There I'd be, glowing in my success, and he would slyly say, "Yeah, but what have you done lately?" Damn! Back to the studio...