So, someone translated:

>「何者{なにもの}にもなれない」

into:

>"Unable to accomplish anything"

That is indeed an ***excellent*** translation in that it conveys perfectly the  meaning/essence of the original.  It is not a word-for-word translation, of course, but a word-for-word translation often makes little sense between Japanese and English. 

「何者」, in ***this*** context with the negative 「なれない」, means "***a worthwhile person***", "***someone who has achieved something***", "***a person worth mentioning***", etc.

「も」 means "even".

「～～になれない」 means "to not become ~~".

Thus, the phrase is saying that **someone is (being) unable to become (even a bit of) a worthwhile person**.

Do you still feel that "***unable to accomplish anything***" is a strange translation?  Quite a few users here seem to let the translated words get in their way of understanding the original.  I know that for sure because I do answer quite a few questions here.

Translation is an art, not a natural science.  The components used in one language do not have to physically correspond to those used in the other.  If the essence of the phrase/sentence is maintained and the product (= translation) sounds natural in the target language, you basically have a good translation.