Indeed, but I wasn't talking about mistakes at all, but specifically about the case when "A understands X better than B does", which is about their mental model of X. I hope you won't dispute that 1) we do say things like that all the time about people, and 2) most of us understand what this means, and it's not just about making fewer mistakes.
Ah, thanks for the clarification; I think I misread you here:
> The weasel word here is "reliably". What does this actually mean? It obviously cannot be reliable in a sense of always giving the correct result, because this would make understanding something a strict binary
What did you mean by "it cannot be reliable in a sense of always giving the correct result", and why would that make understanding something a strict binary?
I do agree that some people understand some topics more deeply than others. I believe this to be true if for no other reason than watching my own understanding of certain topics grow over time. But what threw me off is that someone with "lesser" understanding isn't necessarily less "reliable". The degree of understanding may constrain the possibility space of the person, but I think that's something other than "reliability".
For example, someone who writes software using high level scripting languages can have a good enough understanding of the local context to reason about and produce code reliably. But that person may not understand in the same way that someone who built the language understands. And this is fine, because we're all working with abstractions on top of abstractions on top of abstractions. This does restrict the possibility space, e.g. the systems programmer/language designer can elaborate on lower levels of the abstraction, and some people can understand down to the bare metal/circuit level, and some people can understand down to the movement of atoms and signaling, but this doesn't make the JavaScript programmer less "reliable". It just means that their understanding will only take them so far, which primarily matters if they want to do something outside of the JavaScript domain.
To me, "reliability" is about consistency and accuracy within a problem space. And the ability to formulate novel conclusions about phenomena that emerge from that problem space that are consistent with the model the person has formed.
If we took all of this to the absurdist conclusion, we'd have to accept that none of us really understand anything at all. The smaller we go, and the more granular our world models, we still know nothing of primordial existence or what anything is.
