At the core of design is a deeply intellectual, methodical, and innovative process.
The truly great designers do not simply 'master' their craft. Mastering implies a set of defined rules and techniques for which you can achieve a high level of proficiency.
For that reason, I sometimes don't like the word mastery. From my undergraduate and graduate school research days, one of the things I loved the most about the academic environment was the ongoing commitment to forging new paths. It was not enough to simply learn the techniques in the textbook and then deploy them flawlessly. That's fine and dandy for solving homework problems and copying examples in the textbook.
But not for discovering groundbreaking research.
What really sets graduate PhD research programs apart from other programs is the experimentation around experimentation. Research methods and studies are always being developed in novel ways to do several things:
People often mistake design with its more expressive, soul-searching cousin - art. (I'd argue there's probably also a process involved there as well, but I'm not an artist.)
However, designs get better due to more rigorous and interesting methods of discovering answers and translating those answers into prototypes, products, etc.
For this reason, an important step here at my design lab is to approach design and process much like a research professor would. I learn about commonly used methods, explore the limits of those methods, and then devise new techniques for discovering deeper insights.
A masterful senior designer can take you far. But a trailblazing, nerdy designer trying to be Einstein may take the work (and the field) to a whole other level.