For non-IT people, it’s hard to understand.
For example, do we have to distinguish male and female washroom? In our private washroom (in our house or apartment unit), there isn’t any difference, am I right?
Can private washroom be used only privately? Can our guests and visitors use it?
In real world, human being needs flexibility. 活人还让尿憋死
For IT people it missed some things:
abstract and interface in inheritance
inheritance vs. sealed
class member vs. static member
value type vs. reference type.