regarding 10,000 hours ... from Moonwalking with Einstein
"What separates experts from the rest of us is that they tend to engage in a very directed, highly focused routine, which Ericsson has labeled “deliberate practice.” Having studied the best of the best in many different fields, he has found that top achievers tend to follow the same general pattern of development. They develop strategies for consciously keeping out of the autonomous stage while they practice by doing three things: focusing on their technique, staying goal-oriented, and getting constant and immediate feedback on their performance. In other words, they force themselves to stay in the “cognitive phase.”...
The best ice skaters spend more of their practice time trying jumps that they land less often, while lesser skaters work more on jumps they’ve already mastered. Deliberate practice, by its nature, must be hard....
Amateur musicians, for example, are more likely to spend their practice time playing music, whereas pros are more likely to work through tedious exercises or focus on specific, difficult parts of pieces...
When you want to get good at something, how you spend your time practicing is far more important than the amount of time you spend. In fact, in every domain of expertise that’s been rigorously examined, from chess to violin to basketball, studies have found that the number of years one has been doing something correlates only weakly with level of performance."
tl;dr
10,000 hours may not make you expert. Constantly increasing the level of difficulty of what you practice/work on might be more important.
I've heard it's both - that you need to constantly increase the level of difficulty of your practice for 10,000 hours. The research, after all, says "10,000 hours of deliberate practice", and deliberate practice is what you describe above.
"What separates experts from the rest of us is that they tend to engage in a very directed, highly focused routine, which Ericsson has labeled “deliberate practice.” Having studied the best of the best in many different fields, he has found that top achievers tend to follow the same general pattern of development. They develop strategies for consciously keeping out of the autonomous stage while they practice by doing three things: focusing on their technique, staying goal-oriented, and getting constant and immediate feedback on their performance. In other words, they force themselves to stay in the “cognitive phase.”...
The best ice skaters spend more of their practice time trying jumps that they land less often, while lesser skaters work more on jumps they’ve already mastered. Deliberate practice, by its nature, must be hard....
Amateur musicians, for example, are more likely to spend their practice time playing music, whereas pros are more likely to work through tedious exercises or focus on specific, difficult parts of pieces...
When you want to get good at something, how you spend your time practicing is far more important than the amount of time you spend. In fact, in every domain of expertise that’s been rigorously examined, from chess to violin to basketball, studies have found that the number of years one has been doing something correlates only weakly with level of performance."
tl;dr
10,000 hours may not make you expert. Constantly increasing the level of difficulty of what you practice/work on might be more important.