You need to be an immigrant in order to understand how humans operate & communicate with each other. Humans basically have an operating system – the sum of their experiences & learning through their years of interaction with their community’s members & cultural artifacts.
The operating system allows them to communicate & understand their community members, because they are compatible – the code/signal XYZ triggers the same mental state for any of them. So when 2 compatible humans (having the same operating system) talk, they understand each other. They can read what the other person’s mental state is, what feelings & thoughts he has.
When you immigrate, you encounter people with a different operating system, & suddenly understand that you aren’t compatible with them. Even if the immigrant master the new country’s language, & is a great communicator, he can talk to others & see their body language, but have no clue as to their mental state. This may seem very trivial & obvious, but the implications are very grave: an immigrant isn’t likely to find real friends in his new community, & will always feel lost & estranged.