anticlimax

US /ˌæn.t̬iˈklaɪ.mæks/
UK /ˌæn.t̬iˈklaɪ.mæks/
1.

phản cao trào

an event or experience that causes disappointment because it is less exciting than was expected or because it happens immediately after a much more interesting or exciting event:

:
When you really look forward to something it's often an anticlimax when it actually happens.