Rayleigh explaining that all living things have the capacity for haki. It's not purely anime magic, they pass it on. But having the ability to do something doesn't mean that you will do it. The biggest pushback I've had to this idea is usually "Big mom had conquerors haki, and the parents we see weren't combatants, so that can't be true" And I still fail to understand that logic, because if Luffy lived a peaceful life, he never would've unlocked it. It's a weapon grasped through desperation and danger , but not all strong-willed people who live through dangerous and dire circumstances unlock it, like Kyros or Wyper.