Many interviewers assume the length of using something on a full time job indicates accumulation… Other interviewers test the depth of your insight.
You know you have insight, mileage, accumulation if/when ..
- ..when you know most of the important and relevant  terms in the lingo. Interviewers often go deeper about a new “construct”, and question its motivation/history and limitations.
- ….if you know the __connections__ between the concepts. Without a mental map, there would be way too many unconnected lingo terms leading to info overload
- ….if you know what new developments are only marginally important to your field, so you can focus on the really important
- ..if you can /separate the wheat from the chaff/滥竽充数/. I think often the real veterans would exchange a secret handshake and acknowledge each other very quickly. Eg: Dad (Tan Jiajian) knows his peers in the domain.
- …. If you can’t quickly separate the wheat from the chaff, then probably you aren’t experienced enough.
- ..when you know you have grown much stronger than a junior person new to the field. How soon this happens is poorly correlated to # years
- ..when your mental “book” has grown thin -> thick -> thin. Eg: math..
- ..when you know you can master a “local” system quickly, thanks to the accumulation /under your belt/. Eg: Avichal Gupta…
As you can see, many of the indications/evidence of insight are related to evaluative discussions (including interviews). I’m not being narrow-minded and focus exclusively on job interviews. No. In any team, very quickly person A would size up person B (and vice versa), and often have a rough number in his head about “how much B knows our shared domain”.
 it’s subjective but I feel 90% of what consider irrelevant is clearly irrelevant.
 this includes new choice, technique, best practice
German said one needs to be in a project for 6Y, but I disagree. I feel a wide range of non-trivial challenges is more important, and I feel we are unlikely to get that by staying in one project.
eg Perl — I used Perl for 3 to 5 years..
eg SQL — I used SQL for many years before GS, but my accumulation was solely in GS!
eg Threading — not much used. Mostly accumulation by reading…
eg option math –
eg C++ — see post on c++IV: knowledge more important than coding experience