You can be cautious around something without being afraid of it.

sure - and people might play semantic games about what words really mean but at some point these concepts blend into each other. hence https://thesaurus.yourdictionary.com/caution

Another word for caution noun

    Careful forethought to avoid harm or risk:
    calculation, care, carefulness, chariness, gingerliness, precaution, wariness. See fear

I guess most people would admit a relation between the concepts, caution seems to me to be admitting there might be something to be afraid of. So to clarify my earlier metaphor with a concrete meaning: I will never understand anyone that acts like there can never anything to be afraid of in the unknown.

And I mean the perfect lack of knowledge is impossible, yes if I definitely did not know anything about something I would not be afraid of possible problems with that thing - how could I?

But we always know a bit even about the 'unknown' even if the thing we know is that there might be something in that unknown thing that would be dangerous to life, as many things in the Universe are like extreme heat, cold, releases of kinetic energy, too much water, or the presence of elements of one sort or another in more abundance than is healthy for us, or life that is similar to life on this planet since much of life on this planet is focused on killing other life on this planet for various reasons. I'm walking in an unknown environment on this planet I might still be afraid because I don't know what large carnivores it has, but I do know it might have large carnivores.

I see where you're coming from. I maintain that caution and fear are different, even if they're related.

My original post was probably too broad to be useful. This topic requires nuance that I didn't express.