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.
The sun could've gone nova 8 minutes ago and we wouldn't know for another 20 seconds or so.
Interesting fact: the sun becomes 1 million tons lighter every second.
Lighter or brighter?
Is brightness ever measured in tons?
Well, we'd know by now