It's an arbitrary amount of time that relatively few people are able to dedicate to any skill. The rare people that do are known as "experts".
But you won't be as "expert" as someone with 20,000 hours. IMO it's a tautological phrase based on your chosen definition of "expert". That's why I dislike it.
Pilots' experience is often measured in hours. 10,000 is nothing special (10 years?), but to a lay person they sure know a lot about piloting, and at a dinner party I'd defer to them as an "expert" on anything to do with flying.
But you won't be as "expert" as someone with 20,000 hours. IMO it's a tautological phrase based on your chosen definition of "expert". That's why I dislike it.
Pilots' experience is often measured in hours. 10,000 is nothing special (10 years?), but to a lay person they sure know a lot about piloting, and at a dinner party I'd defer to them as an "expert" on anything to do with flying.