Their job is to deal with criminals, to see crime, to find crime, to fill a quota of crime stopped.
But the thing is that crime can't be eradicated. As long as there are people who want to control, people who want to exploit loopholes around that which is controlled and people who just don't give a fuck, being a police officer is a thankless job and an unavoidable spiral towards falling into the worst this world has to offer.
Every bad thing you can think of, they have to deal with preventing it, seeing it happen or settling the aftermath. And it gets to them. It gets to everyone.
Like, every bad news we see here, reading or watching it from a screen, they deal with them every day, live. And you can see how much it affects people here, let alone those directly involved.
The life of a police officer is not a happy one. It's not a stable one. It's not a safe one. They live in (paranoid) fear that every criminal they meet might have a gun or a knife and will attack them. They see the results of every assault or accident and have to live through the powerlessness of being unable to change it. They are the poster child of what happens when you give a gun and a position of power to someone who's depressed or suffering PTSD.
The ugly truth is you don't want to be a police officer because it will absolutely fuck you up.