Earlier quoted context omitted.
Aren't all hobbies just time-killing activities, though? Is obsessiveness (or worse, the technique of obsessiveness) a useful measurement?
My issue is that since all hobbies are time-killing activities that time ceases to be a useful measure. The majority of people who spend 10,000 hours doing something eventually become skilled or knowledgeable at that thing - but not always. If you remain poorly skilled and not very knowledgeable on a thing after 10,000 hours I'm going to assume those hours were spent "casually" and not with a lot of focus to learn an…
Another thing I've observed is that people who have committed their 10,000 hours and become really, really good are often in doubt about their own abilities. That's because they notice things that less experienced people do not. After 35 years of playing guitar, I feel I know less about it now than I did when I'd been playing for two years. The sense of scope of what I don't know is overwhelming sometimes.