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.
Allowing for quantum randomness does not help the free will argument. Randomness might be “free”, but it is certainly not but “will”.
But it does. If the universe was deterministic, choice would be impossible because all outcomes would be predetermined.
Quantum randomness may not directly provide free will but it does exclude determinism, which would make free will impossible.
This “choice” is just the manifestation what you are at that moment, the sum of everything that has influenced you up until this point. Whether that complex tangle of cause and effect was “determined” a million years ago or affected by random fluctuations the whole way, including a moment ago, doesn’t change anything. “Free will” just doesn’t make any sense, regardless of whether one considers predeterminism to be the alternative.