大意失荆州
dà​yi​shī​jīng​zhōu

to suffer a major setback due to carelessness

  1. 大意 dà​yi
    careless
    Careless; negligent or inattentive; lacking focus on detail
  2. 失 shī verb
    to lose
    to lose; to misplace; to no longer possess something
  3. 荆州 荊州 jīng​zhōu
    Jing Province
    One of the thirteen provinces (刺 cì史 shǐ部 bù) of the Han dynasty, covering present-day Hubei, Hunan, and parts of Henan; a strategic region during the Three Kingdoms period