The etymology of the word expert from etymology online…
expert (adj.)
late 14c., "having had experience… directly from Latin expertus (contracted from *experitus), "tried, proved, known by experience," past participle of experiri "to try, test," from ex "out of" (see
ex-) + peritus "experienced, tested," from PIE *per-yo-, suffixed form of root
*per- (3) "to try, risk."
As opposed to just having knowledge or information from having only read or been told the actual validation for being an expert only comes with moving past received knowledge and by trialling and experiencing for the self. I suppose the risk mentioned is you then allow yourself the opportunity to realise your researched knowledge base and assumptions can just be wrong… that you have tested truly and you observe the limits of both your knowledge and your experience.
There are guys here who know a lot about specific things but being expert is specifically subject matter limited. In teaching being a SME (subject matter expert) maps to a very specific set of criteria (unit by unit based rather than a whole of course expertise). As a scientist I’m sure you completely get that Al.
I always find it disappointing when people with some genuine specific engineering or science background or expertise with a very niche limited range of experiences and preferences use this as some kind of justification to bluff and puff up and stretch their expertise well outside of their actual knowledge base and real expertise and experience.