I knew it long ago: I'm a compulsive teacher, but I can't teach. The godawful state of today's education system isn't what's stopping me. I lack at least two of the essential qualifications.
I cannot "suffer fools gladly." The smartest of my pupils would get all my attention, and the rest would have to fend for themselves. And I can't handle being interrupted.
Writing is the answer. Whatever I have to teach, my students will select themselves by buying the book. And nobody interrupts a printed page.

Foreword: Playgrounds for the mind - N-Space (1989)