I'm sure a large part of it is improving your memory, but the very best in the world probably had some advantage to start off with. For example, if you start o

I'm sure a large part of it is improving your memory, but the very best in the world probably had some advantage to start off with. For example, if you start off learning a language, there are all kinds of tiny details to pronunciation that you don't even recognize and could never recall afterwards. If you try to repeat what someone's said, you might miss a lot of those details. But if you've become fluent at a native (or near-native) level, you've trained your brain to subconsciously recognize and focus on all of those details and can recite something that someone's said perfectly.