駄目
だめ no good; not serving its purpose
Why it means this
駄 (worthless) + 目 (a point on a go board) — from go, a 'dame' is a point worth nothing to either side; hence 'no good, useless, hopeless, must not' (駄目押し, an insurance run; 駄目元で頼む).
Breakdown
Each character links to its full entry — origin story, stroke order, and readings.