- high concentration and
- leaving your comfort zone.
Do you think that Paul McCartney struggled with composition for 10,000 hours in order to write his song Yesterday ?
In other words:
The 10,000-hour rule may be applicable to some performers, but not to all creators.
Speaking of creators, the claim about the need to step outside your comfort zone is also questionable. Young Paul McCartney did not waste his time trying to compose sonatas and symphonies.