What's some things you thought were obvious that most people around you don't?

I recently came across a video with a mother with her 2 sons who looked different but she said they were twins. The comments were super confused, saying that it was probably 2 different fathers, and some claimed the mother already said they were both adopted.

However this genuinely baffled me, bc no one thought they could be non-identical (fraternal) twins. When 2 separate eggs are fertilized by 2 separate sperm cells(not 2 completely diff sperm btw). This is due to the fact that I, myself am a non identical twin. The crazy thing is, non identical twins are apparently more common (according to my quick research to make sure I wasn't missing anything) yet ppl just didn't know. Also I only have one bio father

This has me wondering if ppl even know identical twins are just one singular egg that split.