Ordinals are hard to grasp for people that know the standard school curriculum, know about countability and uncountable sets, cardinality, and the basic propert

Ordinals are hard to grasp for people that know the standard school curriculum, know about countability and uncountable sets, cardinality, and the basic properties and arithmetic of cardinality. I don't know why would it be hard for people that haven't been familiarized with a similar but different concept?