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.
That catch is, you need to find that someone in the first place, and that takes a bit of looking around. So in effect, soul mates are found.
You find a partner, who then MAY become a soul mate