Tatami etiquette: Why you should never step on the threshold of a washitsu Japanese room soranews24.com

But did you that when visiting someone’s home, it’s considered rude to step on the threshold of the doorway to a tatami room?
Even foreigners might get some serious side-eye if they’re seen doing it, though we’re given a bit more slack, since we don’t know any better.
Even Japanese people don’t know exactly why such a rule exists, but there are several theories.
As such, stepping on the threshold doesn’t respect that boundary and violates the sanctity of the space.
When the light was blocked out, they knew someone was standing on the threshold, and they used that opportunity to strike.