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 speed of advancement from the industrial revolution to present.
The relatively short time humanity has been around
The universe is finite but expanding
The Monty Hall problem
The absolute scale of devastation created by humanity
I may be wrong but I thought it was generally believed that the Universe is infinite (or at least that that was the most common belief among those that are qualified in the field)
Edit: I mean infinite in Space, of course it hasn’t existed forever
Edit2: I quickly read this article https://www.swinburne.edu.au/news/2021/08/Is-space-infinite-we-asked-5-experts/ where the 3 astronomers answered maybe, yes, and yes. Whereas the two non-astronomers answered no. Since this seems to agree with me I will believe that this is correct and not investigate further
The funny thing is that sounds exactly like what he would say.
We humans are roughly as big compared to atoms and subatomic particles as we are small compared to the largest structures of the observable universe