"The story was supposed to be that of a child who, after a tantrum, is punished in his room and decides to escape to the place that gives the book its title, the "land of wild horses". Shortly before starting the illustrations, Sendak realized he did not know how to draw horses and, at the suggestion of his editor, changed the wild horses to the more ambiguous 'Wild Things'..."

I love that illustrators not wanting to draw horses is such an ubiquitous thing it led to the creation of a classic children's book.

quote via Wikipedia https://en.wikipedia.org/wiki/Where_the_Wild_Things_Are