useless messenger; fool's errand; doing only as told
Idiomatic expression describing a person sent on an errand but unable to act independently, or the errand itself as a pointless task.
Even if I left it to him, it was like a fool's errand, and I ended up doing it myself.
そんな簡単な交渉もできないなんて、まるで子供の使いだ。
Not being able to handle such a simple negotiation is just like a useless messenger.