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.
Ah, I see what you mean - that the superposition is a model of our uncertainty of unobserved actions, rather than the actual state of the particle. While that was my understanding initially too (because it makes sense) our testing, things like the double slit experiment, has shown behaviours that only make sense if they do occupy both states simultaneously. Quantum computing is actually reliant on qubits being in a 0/1 superposition for it to work. It's what makes the entire thing so maddening, because experimental evidence has disproven every attempt to make it make sense.
First thing my quantum mechanics professor told us was that if you think you understand quantum mechanics you definitely do not understand quantum mechanics. He was at the time one of the world's leading experts on quantum applications, and had just proven the existence of an additional state of matter that quantum theory predicted, and straight up told us to our faces that he didn't understand it, he just knew that it works.