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 might be misremembering but I believe our sun can’t go nova, it’s too small. It will, however, expand and swallow the Earth towards the end of its life.
When exactly would that be? I gotta add it to my calendar.