Well, I’m not sure, but what I got from the dictionary for 自負心 was 「自分の才能に自信や誇りをもつ心。」. For 誇り, it’s 「ほこること。名誉に思うこと。」I’m just noticing that 「自分の才能に…誇りを持つ」is a valid structure, so it seems 誇り is actually quite a general word, just like プライド. I have to admit that I don’t really know what the verb 誇る means, since I haven’t seen it often enough (and I’m not completely sure what the terms used in its Japanese definition mean), but I’m also not sure 仕事 counts as a type of 才能. I guess I’ll become more ‘sure-footed’ as I go along. Today’s the first time I’ve seen 自負心 after all. However, the pride-related definition of 自负 in Chinese is ‘believing that no one can equal oneself’, which sounds pretty close to the Japanese definition.
What surprises me is the lack of a Sino-Japanese word as well. I mean, sure, the kanji is still based on Chinese usage. That’s true. However, the 和装本 look a lot like the books depicted in Chinese period dramas, so I’m just surprised that Japanese didn’t just keep 丁. For that matter, while I’m not entirely sure about historical Chinese usage and its influence on Japanese usage, but my Chinese dictionary says 頁 was used as a counter for the pieces of paper in traditional books, which is probably where the Japanese counter 頁（けつ）comes from. Today, Chinese uses 頁 for one side of a page (as opposed to one page, which was the historical usage). I guess my question is, why introduce a new word when the concept really isn’t too different? Even now, 頁（けつ）is listed as a synonym for ページ when used as a counter. 丁 could have been reserved for single sheets, while 頁（けつ）could have been used for single sides. Chinese just has 页, and it’s used to mean both. Maybe I just find it strange that the language with more words available chose to adopt a completely new one, whereas the one with fewer words just increased the number of possible meanings. Well, can’t change history. Perhaps I’ll just try to find out when ページ entered Japanese. If it happened during the Meiji Restoration, then I won’t be as puzzled anymore.