Joshu, a novice monk in a Zen monastery, was feeling hungry for some cake. He went to the abbott to ask for permission. Normally, the abbott wouldn’t allow such indulgence, but instead he said to Joshu that he could, if he followed the abbott’s recipe. Joshu agreed to this term, and went with the abbott to retrieve the recipe.
When the abbott gave Joshu the recipe, he quickly scanned it to get a feel for what kind of cake it would be. It had all the standard ingredients for a white cake of some sort, except one of the ingredients was listed as “cake.” Joshu respectfully pointed out the strange ingredient, and asked how this could be. The abbott cheerfully replied that it must have been a mistake, and crossed it out. “You can make it now,” he said.
Joshu thanked the abbott and proceeded to the kitchen, still confused as to how cake could appear on the recipe. When he went through the recipe, mentally checking off the ingredients as he used them, he finally got to the crossed-out “cake,” and it occurred to him again what the abbott said before he left: you can make it now; cake is possible only without “cake.”