Self control is a finite resource:

Self-control is a finite commodity that is depleted by use. Once the pool
has dried up, we’re less likely to keep our cool the next time we’re faced
with a situation that requires self-control.

This is also why self-control strategies for coping with addictive urges
very often break down, according to Dr. Marc Lewis

Here are some brain scan images

*This is Your Brain on No Self-Control*