At the age of three or four a child begins to ask the question, "Why?" In so far as we can think our way into the mind of a child, we might say that he is trying to understand the world around him and meets with puzzles that he cannot resolve. He is seeking an explanation. This word derives from the Latin planus, which means "flat" or "smooth." Explanation renders smooth that which formerly had been rough or uneven. Before a person seeks an explanation he must be aware of something rough or uneven, something troublesome in the flow of experience. The explanation, when accepted, removes that rough spot and renders the flow of experience once more smooth.