run out of gas

(verb) to lose energy or interest

Example Sentences:

A: Are you still enjoying your Art class?
B: No, I’m really running out of gas. 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 gas and had to take a break.

Tiffany ran out of gas while studying for her final exam, and fell asleep at her desk.

From the Blogs:

Has Hydrogen Run Out of Gas?

Media:

Similar idioms:

1. run out of steam
2. run over
3. run across (2)
4. run across
5. make-or-break
6. run of the mill