Lewis had a remarkable memory for what he read of others, but sometimes his memory of his own writings failed him. Though he had a large library, he did not keep all of his own books there!  Walter Hooper adds, “Often, when I quoted lines from his own poems he would ask who the author was.  He was a very great scholar, but no expert in the field of C.S. Lewis.”

(As quoted in Seeing Beauty and Saying Beautifully, by John Piper)