For me it is the fact that our blood contains iron. I earlier used to believe the word stood for some ‘organic element’ since I couldn’t accept we had metal flowing through our supposed carbon-based bodies, till I realized that is where the taste and smell of blood comes from.
I can really relate to this. I remember a weird night in my teens where I must’ve spent at least an hour staring out of my bedroom window at the moon, because really for the first time I’d had the exact same thought. It’s right there. It’s so easy to get desensitised to that and to just think of it all as an image projected on the sky. The thought has never really left me and even now I still linger on the moon every time I see it and try to acknowledge that it is a 3 dimensional object lol.
The fact that the moon is tidally locked probably doesn’t help, if it rotated it would be easier to see it as a sphere instead of an image