A monk asked Ikan, a student of Baso, "has the dog Buddha-nature or not?" Ikan said, "Yes." The monk asked, "Have you it or not?" Ikan said, "I have not." Monk: "All existent creatures have the Buddha-Natures; how is it that you have not?" Ikan: "I don't belong to all existent creatures." Monk: "You say you don't belong to all existent creatures. This 'You', is it a Buddha or not? Ikan: "It is not a Buddha." Monk: "What sort of thing, in the last resort, is this 'You'?" Ikan: "It is not a thing." Monk: "Can it be perceived or thought of?" Ikan: "Thought cannot attain to it; it can not be fathomed. For this reason, it is said to be a mystery."
-Blyth's Mumonkan, Case 1
Ikan wasn't bothered by the question, "Who am I?" Why is anybody bothered by it?