故

Right side is the four-stroke action radical — a stylised hand holding a stick, marker for striking, governing, causing. In 故 it pins the abstract sense: a cause is something that produces an effect, an old story is something handed down by deliberate transmission. Same radical in 教 teach, 改 change, 政 government — all acts of bringing about.

Left side 古 supplies the sound — gǔ shifting to gù, just a tone change. 古 itself depicts ten generations of mouths handing down words (十 + 口), the picture of antiquity. That nuance reinforces 故 beautifully: a 'reason, cause, old story' all draw on the same flavour of inherited fact. Same phonetic in 估 estimate, 姑 aunt, 苦 bitter.