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 remember my parents talking about some thing or other in star trek that would be impossible because you’d need “terabytes of storage, and that’s probably not possible”. And now you can go buy 1 tb of storage and lose it in your couch cushions.