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.
How about the new 2Tb m.2 drives? Not only vastly larger yet still, transfer speeds are also insane. I once had a computer with a 20Mb hard drive, current drives transfer 600-1200mb per second.