In the late second century, which was the Eastern Han period, Liu Biao, was the military governor of Jingzhou, in now Hubei province. His elder son by his first wife, Liu Qi, was worried that his stepmother, also the mother of his stepbrother, hated him and conspired against him for fear that he might take over his father’s power after his death. Liu Qi turned to Zhuge Liang, the military advisor to his uncle Liu Bei for help. Zhuge Liang at first was reluctant to openly help Liu Qi because he considered it Liu Biao’s domestic affairs.
One day Liu Qi invited Zhuge Liang to his house for a visit. He told Zhuge Liang that he had some rare book collections in his private library on the second floor and he would very much want Zhuge Liang to go up there and take a look. After both of them were on the second floor, Liu Qi had his servants remove the ladder and said to Zhuge Liang, “Now there is no one here but you and I. Please tell me what to do to cope with my stepmother’s conspiracy.” Zhuge Liang then told Liu Qi to go asking his father to let him be the garrison commander of a remote outpost so that he would stay away from the trouble his stepmother might get him involved.
Cu Ti Yan (去梯言), literally the words after the removal of the ladder, becomes the synonym for a secret or private matter told to someone under a condition of trust.