3 sentences

1. 这次失败是一个惨痛的教训。

   zhè cì shī​bài shì yī gè cǎn​tòng de jiào​xun.

   This failure is a bitter lesson.

   Source: Dong Chinese Dictionary

2. 这是我们15年来最惨痛的失败。

   zhè shì wǒ​men15 nián​lái zuì cǎn​tòng de shī​bài.

   This is our worst failure in 15 years.

   Source: OpenSubtitles

3. 想到往事，他内心感到十分惨痛。

   xiǎng​dào wǎng​shì, tā nèi​xīn gǎn​dào shí​fēn cǎn​tòng.

   Thinking of the past, he felt a deep sense of grief.

   Source: Dong Chinese Dictionary