What is the origin of the idiom "have something down pat" and when to use it?

The idiom "have something down pat" suggests that someone has mastered a skill, task, or knowledge to the point of being able to perform it perfectly and effortlessly. It originates from the idea of having a pattern or process down so well that it feels like it's been imprinted or memorized, akin to having it "pat" or perfectly mastered. This phrase is commonly used to indicate a high level of proficiency or expertise in a particular area, emphasizing that the person is highly skilled and knowledgeable about the subject or task at hand.