Because the life of a foreigner is normal to the foreigner, the foreigner forgets that other people live different lives.
Take these two fairly ordinary statements, excuses in this particular instance.
For some reason everyone understands the first one but the second one causes no end of confusion. They are of equal weight around here. Both are common enough experiences in the great scheme of things. The statements are simple enough, but they convey a whole panoply of commonly shared human experience.
1. Sorry I'm late but she broke her finger.
2. Sorry I'm late but he's gone all nocturnal.
And sometimes not!
In the interests of scientific impartiality, I shall have to try them out again in England, when we nip home for a holiday. A good scientist never predicts outcomes prior to the test.
Verily, I shall be a foreigner on either shore.