I don't know.

I can tell you what it takes to evolve from Beginner to Intermediate: having many conversations with everybody at your club, reading magazines and books, surfing the net, building and flying much and trying things that make you feel out of your comfort zone while trying to understand the physics behind those things, and over any other thing, becoming passionate about model airplanes and flying.

Now, I would be afraid of becoming an expert, because I feel that such believe would close the doors to keep learning and trying new ideas. May be I am wrong.

Here are some quotes about Experts:

“If your mind is empty, it is always ready for anything; it is open to everything. In the beginner's mind there are many possibilities; in the expert's mind there are few.” Shunryu Suzuli

“Always listen to experts. They'll tell you what can't be done and why. Then do it.” Robert Heinlein

“My definition of an expert in any field is a person who knows enough about what's really going on to be scared.” P. J. Plauger
“An expert is a person who has made all the mistakes that can be made in a very narrow field.” Niels Bohr