run out of steam
US /rʌn aʊt əv stiːm/
UK /rʌn aʊt əv stiːm/
1.
to lose energy or enthusiasm and stop doing something, or to become tired and less effective
:
•
The project started strong, but it seems to be running out of steam now.
•
After working for ten hours, I started to run out of steam.