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.
It’s actually interesting because when you consider the four fundamental forces of nature (gravity, electromagnetism, strong nuclear, weak nuclear) gravity is by far the weakest one. It’s not intuitive because gravity is the one we interact with most day to day and it has connotations of large objects like planets and stars. But it’s only a significant force when you have such large objects. Two magnets technically are gravitationally attracted to each other (like all things that have mass) but it pales in comparison to the magnetic forces.
Gravity makes up for what it lacks in force with its range and also the exponential nature from things getting attracted to each other forming a point of more potent attraction and so on (it was more relevant in the beginning of the universe, but we’re still feeling its effects)