The point is that if you were trained in your domain, you can't hold yourself up as an example of "an imposter who had to learn it all themselves" because some of it was given to you as "absolute" knowledge. That you weren't "trained" in some 'basic tasks' (and some people are - imagine the boy scouts, preparatory schools or the military) doesn't mean you had to "imposter" your way into learning everything else - you simply learned those "by osmosis". (Otherwise, we'd have thousands of different ways of accomplishing each of those basic tasks in use.)

Social interactions are informed by past interactions, in a sort of "telephone game" through time and society (which is why trends evolve and change). And we aren't trained how to do taxes because there's an entire industry devoted to profiting off them which lobbies to keep it feeling complex and against just having the IRS send you a form to sign or dispute.