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.
First time I saw Jupiter through a telescope I got hit hard by the feeling: “Oh shit, that giant monster is real”.
Samesies. You aren’t alone. We have a support group.