This is common sense.
As a linguist says, "Languages will decrease their complexity as they are used".
In my opinion, "Frequently used languages are often not primary languages for their users, so learning should be easy. If that is difficult to learn, that language is not used.".
I think that this is true even if language is replaced with common sense.
In other words, common sense of a group that accepts diverse individuals is easy to learn.
Common sense means a premise that individuals do not need to check again, common sense is deepened if the target group is close.
I think Japanese people have national character who values common sense.
People notice that common sense does not have the same meaning everywhere if everyday life is full of diversity.
It is hard to say that Japanese society has sufficient diversity.
So, the common sense of Japan is difficult to master for foreigners, and even speaking, Japanese people can not understand the common sense of fixed groups of Japan.
For Japanese people, common sense is a vested interest.
We Japanese deal with passengers who are customers carefully, but may not let go of them to foreigners threatening their position in work.
This actually happens in other countries as well, even between Japanese people.
SAYONARA.