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.
Albeit arbitrary… if it’s globally recognized that each new day begins as the sun crests the international date line, and the sun indisputably rises from the East, why would it not make sense?