adverb · used at the end of a rhetorical question to imply 'can it be that...?' or 'is it possible?'

难道你还没听懂不成？

adverb · to fail to complete or achieve something; unable to

这件事我看是办不成了。

adverb · to be unacceptable, inappropriate, or out of the question

如果他不答应，那可不成。