The definition of run out of steam is:
(verb) to lose energy or interest
A: Are you still enjoying your Art class?
B: No, I’m really running out of steam. The teacher is boring and I hate art.
A: Perhaps you should’ve chosen a different course.
After running for 10 km, Robert started to run out of steam and had to take a break.
Tiffany ran out of steam while studying for her final exam, and fell asleep at her desk.
From the Blogs: