You say arigatou to be polite. It was never about politeness.

The word comes from Buddhism, from 有り難し, arigatashi. Broken apart, it means 'difficult to exist'. Something that has to exist, but rarely does.

So 有り難い, arigatai, came to mean rare and precious. Not thanks, but wonder. A thing so uncommon that when it happens, you almost cannot believe it.

The old Buddhist texts used it for the rarest thing of all: being born a human, awake and alive. An old Buddhist text opens with it. To even be here is 有り難い.

So when you say arigatou, you are not being polite. You are saying: what you did for me almost never happens. Thank you for the miracle.

Say it slower tomorrow.

Sources: 日蓮宗ポータル; 法句経.

manamana_nihongo