Catchphrase of Chinese flash-sale culture. The Taobao / JD app literally pops up 手慢了 on screen when you tap 'buy' on a 秒杀 item one beat after sellout. Also a fixture of WeChat group 红包 (red envelope) grabs and livestream limited drops.
grammar
Subject 手 'hand' + adjective 慢 'slow' + 了 (change of state). Literally 'the hand was slow' — the hand is taking the blame for the brain's reaction time. Pair with the antonym 手快 'quick on the draw'.
