Graphics designing is not just about knowing how to use graphics editors or softwares. It is not the technical know hows of such an editor that automates design tasks. Graphics editors are only tools used to process and materialize the design concept. A design starts from an idea or concept from a single person or from a collaboration of few people and it may evolve as the process goes.
Love
To master the art is to love the art, in other words, love what you do. Keep on doing the art frequently because practice makes perfect and doing is also learning. By doing consistently, anyone at any point will discover new knowledge, skills, and techniques.
Imagination
Designing in general also requires a strong sense of imagination. Anyone can do this, imagining things before fulfilling or thinking about the outcome first. There is no limit on what a human mind can think of. Designers of fantasy art does this very often and when they do, their fantasies will turn into ideas or concepts. Any sort of graphics editors can only produce usable and really nice art with the help of playful imagination of a designer. Even the least powerful graphics software can do better with a good designer.
Communication
In designing for a business or for other people, the design will start from a scratch and the concept will be a result of brainstorming together with the client and the designer or designers. In short, a master of graphics designer must also know how to communicate and interact with clients and co-designers. By the way, an art or design itself is another form of communication.
These are just the most basic requirements to master the art of graphics designing but if you can have it, then you can start to master graphics designing.