Zhè diǎn shì dōu bàn bu chéng, zhēn chéng le xiāhuǒbīng.
If he can't even handle a task this small, he really has become a dud.
Tips
memory
瞎火 is a dud shell — one that won't fire. A 瞎火兵 is a soldier no longer fit to shoot back. Pointed military image, now used more broadly for someone who's lost their edge.