He could have won in this competition, but he did not join. That made him regrettable.
Examples (Wiktionary)
Mandarin
她很后悔当初没有学好英语。
她很後悔當初沒有學好英語。
tā hěn hòu huǐ dāng chū méi yǒu xué hǎo yīng yǔ .
She regrets not learning English well from the outset.
Mandarin
好多观众都说,你的“实话实说”后来没有之前做得好,我只能笑笑,如果他们看到当初我做的节目,还说好的话,我“崔”字倒过来写。
好多觀眾都説,你的“實話實説”後來沒有之前做得好,我只能笑笑,如果他們看到當初我做的節目,還説好的話,我“崔”字倒過來寫。
hǎo duō guān zhòng dōu shuō , nǐ de “ shí huà shí shuō ” hòu lái méi yǒu zhī qián zuò de hǎo , wǒ zhǐ néng xiào xiào , rú guǒ tā men kàn dào dāng chū wǒ zuò de jié mù , hái shuō hǎo de huà , wǒ “ cuī ” zì dào guò lái xiě .
Many viewers have said that I never did anything as good after Straight Talking. I can only laugh. If they look at the program now as it was back then and still think it's any good, I'll eat my hat (lit. I'll write my surname of "Cui" upside down).