2 sentences for 失望 (shī​wàng — lose hope)

1. 不要失望。

   bù yào shī​wàng.

   Don't be disappointed.

   Source: Tatoeba

2. 由于连续的失败，他对手头的项目彻底失望了。

   yóu​yú lián​xù de shī​bài, tā duì shǒu​tóu de xiàng​mù chè​dǐ shī​wàng le.

   Due to consecutive failures, he was completely disillusioned with the project at hand.

   Source: Dong Chinese Dictionary