Lock the stable door when the horse is stolen. 贼去关门。
The jeweller had been burgled twice in a year before he decided to install extra security devices, but it was a case of locking the stable door after the horse has bolted. 这个珠宝商一年内被偷窃两次后才决定安装特别的保险装置,这是一个贼去关门的事例。