system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If adrenaline boosts our mental quickness and physical strengths, how come it isn't always pumping through our veins?
gpt
It’s unsustainable, basically.   This is kinda like asking why you don’t sprint everywhere - it’s faster, isn’t it?   Because it’s *exhausting*, and you wouldn’t be able to keep it up.  

Our bodies aren’t designed to be running at absolute maximum capacity like that.   The adrenaline surge is an emergency measure, designed to get us out of trouble if we need it.  Very useful if you need a burst of speed to avoid a lion, or extra strength to wrestle a fallen tree off your toddler, but you don’t need that when you’re playing video games or hanging out at the pool.   

It is also pretty damaging to be in that state.   Adrenaline is not good for you, not long-term.   There is actually a maximum amount of time you can sustain the heightened state of adrenaline before it tapers off - even if the situation hasn’t changed.   This is because you run out of adrenaline, and also because your body literally cannot maintain the high alert state for more than a few hours *max*.   There is a longer-term, less extreme stress hormone called cortisol that takes over if the stressful situation is lasting longer than that.