It may be worth mentioning that sometimes Vて しまいました is sometimes shortened to Vちゃった.
Literally, しまう means "to finish." Do not be surprised to find this word used only in this meaning sometimes, with no "undesired"-connotation.
-てしまう - sometimes contracted to ちゃう
The title should be "shimau" instead of "teshimau." "te" is a particle and does not form the root of "shimau."
Wouldn't this fall under the other category of しまう？「その映画を見て泣いてしまった」にはほかの翻訳あると思いますが。。。 Watching that movie, I cried (not that I wanted to, or expected to cry). Perhaps because this would be a case where there isn't regret?
I think 〜てしまう can imply two meanings: 1) completed 2) to my regret I'm really not sure how one can distinguish which one a person is trying to imply.. I guess it's based on the context of what one is saying?
I agree with eastmael. Here is some explanation from text : 〜てしまう １．全部終わる E.g. : 作文をかいてしまったら、公園に行きましょう ２．失敗する・残念だと思う E.g.: 1.大切な結婚指輪を無くしてしまいました。 2.大好きな猫が既に死んでしまったんだ。 I think if something bad happened unwillingly, 〜しまう goes to the 2nd meaning.Otherwise, if it is something done without any special adverse effects or just a plain task or action, it goes to the 1st meaning.
I don`t know about everyone else, but I have never heard しまう used to mean "I finished Ving" It always seems to have a negative meaning attached to it.
Tigertさん, I added example #6786 caught from JPLT2 in this level 3 entry exactly for the note you wrote.
I'd like to offer a more natural translation of the sentence beginning with 前から欲しかった本。。。 I got a book I had craved for a long time, so I immediately began reading, and read all night long until I finally finished it.