There's also grit. Which means never ending dedication even through difficult times. It basically means that becoming better is your primary goal in life. Everything is secondary to you improving your skills in your life.
Mediocrity can always be achieved via the join of two existing skills (if you know A and you know B, then doing C is "just" doing both A and B at the same time), but greatness requires leaps (if you know A, but the path from there to B doesn't involve any combination of other existing skills, you'll just have to try a bunch of stuff until the penny drops/inspiration strikes/the muse vists/etc.)
(being mediocre myself, I can't speak from personal experience, but this is certainly how it looks when regarding the acknowledged [Nobel/Olympic/Turing] greats with whom I have studied/trained/collaborated over the decades)
B/ Consider Niels Henrik Abel's opinion on whom to study.