(mathematical subject is intended)
It's obviously not a simple question, but I thought it could lead to some interesting discussion. I was reading Lewis Campbell's biography of James Clerk Maxwell and he mentioned somewhere that when they started learning Euclid at school, Maxwell's peers (Campbell included) could feel that Maxwell was already at the heart of the subject, while they were all on the edge. I have felt this myself many times (being on the edge; almost not being able to bridge the gap between an artificial understanding and a "creative understanding"), and I am really interested in how it is that someone reaches the heart of a subject. I don't know how to define this, but it's usually when they can give simple proofs that you couldn't even dream of giving. The proofs have this magic property about them, such as auxiliary lines that seem to drop out of nowhere. Such minds are able to pursue successful research in the field. They have a full command of the subject even very early on, as in Maxwell's case for instance.
This might seem like a vague question, but I have tried my best to give a feel of what I really mean, so I hope we can get a other people's views on this.
NOTE: If you understand what I mean and have a better way of phrasing the question please leave a comment, I really don't want this to get closed because of my bad wording.