一失足成千古恨

yī shī zú chéng qiān gǔ hèn

a single slip may cause everlasting sorrow (idiom)

one

shī

to lose

(bound form) foot; leg

chéng

short name for Chengdu 成都[Cheng2 du1]

qiān

used in 鞦韆|秋千[qiu1 qian1]

ancient

hèn

to hate