He writes that if one over-learns and then over-relies on technique it's quite possible one will never develop self-expression. On the other hand, focusing on self-expression before having developed the tools to adequately express oneself leads to childish work.
He ends his essay with this: "But both are necessary, and it is only when what can be taught, is working in perfect harmony with what cannot be taught, that a work of art results."
As we entered a break for the holidays, I set a task for my drawing students. Find an object that is near and dear to your heart. Set it up, light it and draw it once. Then draw it again. Then again. Fifteen, eighteen, twenty-three times. Draw until what is coming out on the paper is direct from your heart - not the result of thinking through the processes we've learned.
Now - you may be delighted with the results - or you may be disturbed. Either way, you've been successful because now your pencil work is you speaking - not what I've taught you. Either way - you've made a huge leap and now your task is to inquire as to WHY you are disturbed or delighted. This is where learning truly begins because now you're learning about yourself.