When does expertise become sufficient to be an expert?

Throughout the session and while we were discussing in large group or in the breakout rooms, that thought did not leave my mind : When does expertise becomes sufficient for someone to be considered an expert in something?

It was not a question te be asked during the session itself, as I know deep inside that there is no clear answer. In theory, we learned together that someone is (or is close to be) an expert when he/she is becoming able to organize information rapidly field into patterns in his/her field of expertise. Also, this information is organized in such way that it is relevant, and not randomly organized like it may be in the novice's mind. Finally, the information retrieval is done in a more automatic manner and only when needed (i.e. not in a painful, laborious way, as we can see in a novice learner). Regarding our job as teachers, in developing expertise, we also learned that we should help our learners to recognize patterns, to join them in their quest of building scripts in their head so they can chunk volume of information, decrease intrinsic cognitive load and facilitate practical information retrieval.

I cannot stop myself to link what we learned with a popular book I have read a few years ago : Outliers, from Malcolm Gladwell. In his book, he writes about success and gets somehow close to learning, to a certain extent. Gladwell discusses also frequently about the idea that 10,000 hours are needed to become an expert. I think that idea may be oversimplified, but it is interesting to notice that it represents approximately the total duration of a medical training and a residency training, or an engineering training combined to the junior trainee years following graduation and certification. However, while we could imagine that aligning 10,000 hours of a certain task makes one an expert, it is also interesting to notice that Gladwell gives examples in his book of professions where several modalities of learning are engaged, like it is the case in medicine... and like what we read in Make it Stick... So maybe it is not as simple as 10,000 hours. And I guess we will learn why in the next few weeks.