How to say regret in the postgraduate entrance examination in ancient Chinese

This situation can be said to be a pity in ancient Chinese.

Regret means: something that you think is not perfect or you are not satisfied with. Postgraduate regret means that you did not meet your own requirements. It can be said to be a regret.

The regret comes from "Liao Chengzhi's Letter to Mr. Chiang Ching-kuo": "I have not heard from him for a long time, so I sincerely regret this. I have recently heard that the government has violated peace, and I am deeply concerned."