difficult matter; tough case
Refers to a problem, issue, or case that is hard to handle or resolve. Often used in business, legal, or bureaucratic contexts.
It hasn't been decided yet how to handle this difficult case.
With tough cases piling up, the person in charge looks overwhelmed.
Compound of 難 (difficult) and 件 (matter, case). The exact historical derivation is uncertain, but the meaning is transparent from its components.