Point of interest: the origin of ありがとう

In modern Japanese it is usually written with kana, but it can also be written with kanji and okurigana in several ways, most commonly

あ

有

り

がと

難

う. This combines

あ

有

る (to exist) with

かた

難

い (difficult), and is descended from the classical adjective form ありがたし, which did in fact originally mean 'extremely uncommon' or by extension 'rare and precious'. The phrase ありがたきもの occurs in one of Japan's earliest novels, The Pillow Book, to mean 'it is hard to live'.

Over time, however, the phrase began to be used not just to express the rarity of an object, but gratitude for the possibility of possessing such a rare object. Over time, it became a way of expressing gratitude generally.

From time to time you may hear the suggestion that ありがとう is connected with the Portuguese word obrigado, which sounds similar, and also means thank you. However, the two words evolved entirely separately - the Japanese word was in use well before any contact between Japan and Portugal, and the Portuguese word derives originally from the Latin root 'obligare' (the origin of oblige and obligation etc. in English).