Wiktionary
fire in the belly
alt. (context idiomatic English) The emotional stamina and vigor, passion, or inner drive to achieve something, to take action, etc. n. (context idiomatic English) The emotional stamina and vigor, passion, or inner drive to achieve something, to take action, etc.
Usage examples of "fire in the belly".
The strength and the heat, that flash of fire in the belly that came just before release.
It's put some fire in the belly of the Hurrians and what's left of their old aristocracy.