Impulses and Inhibitions

Impulses occur from the limbic / survival brain, which prioritizes speed over accuracy. None of it has to be rational, what matters is surviving first and sorting it out later. The more stress and / or tired we feel the more impulsivity we experience, as a result of losing inhibition strength. 

Inhibitions are what we use to curb impulsivity, and inhibitions occur from the PreFrontal Cortex part of the brain, which is deactivated by stress.

Think of the balance between the two this way: As a survival based organism the human body has unlimited access to impulsivity to aid survival, however only a limited amount of inhibition strength to aid higher mind logic and objectivity. 

We experience endless impulses in combination with a limited amount of inhibition strength.