It's true, although they changed the medium: https://news.ycombinator.com/item?id=19960342
> James Clear reached out to the authors of Art & Fear and this is his footnote: https://jamesclear.com/repetitions
> This story comes from page 29 of Art & Fear by David Bayles and Ted Orland. In an email conversation with Orland on October 18, 2016, he explained the origins of the story. “Yes, the 'ceramics story' in Art & Fear is indeed true, allowing for some literary license in the retelling. Its real-world origin was as a gambit employed by photographer Jerry Uelsmann to motivate his Beginning Photography students at the University of Florida. As retold in Art & Fear it faithfully captures the scene as Jerry told it to me—except I replaced photography with ceramics as the medium being explored. Admittedly, it would’ve been easier to retain photography as the art medium being discussed, but David Bayles (co-author) & I are both photographers ourselves, and at the time we were consciously trying to broaden the range of media being referenced in the text. The intriguing thing to me is that it hardly matters what art form was invoked—the moral of the story appears to hold equally true straight across the whole art spectrum (and even outside the arts, for that matter).” Later in that same email, Orland said, "You have our permission to reprint the any or all of the 'ceramics' passage in your forthcoming book." In the end, I settled on publishing an adapted version, which combines their telling of the ceramics story with facts from the original source of Uelsmann’s photography students. David Bayles and Ted Orland, Art & Fear: Observations on the Perils (and Rewards) of Artmaking (Santa Cruz, CA: Image Continuum Press, 1993), 29.