When I teach firearm classes one of the things I stress is the difference between accident and negligence. In today's enlightened society we seem to be unwilling to assign blame in many cases and disregard personal responsibility. We call them "car accidents" not "car crashes". Cars only crash when one or more parties involved have made an error. We cry out against evil banks banks and title loan places lending money but don't hold those people borrowing the money they know they can't pay back accountable. I could go on and on, but won't. This time anyway. :-)
Pay attention to this sentence- If a firearm you are handling discharges unintentionally and damages property or a person you have been negligent. It's not an accident, it's not an oops, it's not somebody else's fault. You have been negligent. It's your fault. You did something wrong.
For the most part if you are handling a firearm and it discharges unintentionally you are negligent even if it doesn't damage anything or hurt a person. Very rarely there can be a mechanical failure when loading a gun or manipulating it in other ways. I know a man whose hunting rifle fired when he took the safety off to unload it. Had he been paying attention to the rules of gun safety he wouldn't have shot out the window of his van. Even though it was a mechanical failure the result was his negligence to keep the gun pointed in a safe direction when he was handling it. I recently read an account of a man that was on a hunting trip and was unloading his gun each time he returned to camp. After chambering the same round 7 or 8 times his rifle fired because each time he did it the firing pin barely dented the primer. After a half dozen times it allowed it to set that primer off.
But those sort of events are rare. Most firearm negligence involves a person pulling the trigger on an "unloaded" firearm. This is a gun a person thinks is unloaded and it isn't. You think a gun is unloaded and you pull the trigger to take it apart. (Glocks require this, btw) You are practicing dry fire in your living room with your carry gun and when you are finished to load your magazine. Then practice one more shot. You are showing off your new gun when you are drunk and put a hole in the wall (or your head).
Every time you handle a firearm you need to follow the 3 rules of firearm safety. Every time. If a friend hands you an unloaded gun check to make sure it's unloaded while pointing it in a safe direction. Every time. It should become a habit, get handed a gun- check to make sure it's unloaded.
It's quite possible to go your whole life without a negligent discharge. I certainly know it's my plan. For most of my adult life I've been shooting at least monthly and my round count is coming up on 50k although I haven't really kept track. I have yet to have a negligent discharge and I have worked to instill habits to make sure I never do.
If you want to see a variety of scary stories just search "negligent discharge" on the internet and you'll be presented with a number of horrifying stories. Don't be one of those people.