Glocks don't have EXTERNAL safeties but they are safe nonetheless. Glock design makes it IMPOSSIBLE for the striker to contact the primer UNLESS A HUMAN FINGER IS PULLING THE TRIGGER.
I added emphasis above. That's obviously not true as any object that manages to enter the trigger guard and press the trigger to the rear while depressing the "safety" will fire the gun. There are documented cases of that.
That said, the majority of cases where guns went off when they shouldn't are due to folks having their trigger digit where it wasn't supposed to be. There are phyisological reasons for some that. These include startle response and sympathetic muscle action.
We’ve all experienced startle response, you hear a loud noise or see an unexpected motion and your muscles tense and you may jump. Sympathetic muscle action is simple, if you tense the muscles of one hand, the muscles of your other hand will also tense, or tense further. In either case, if your finger is on the trigger, you may well hear the loud noise of a negligent discharge.
There's also another factor to consider, it's called trigger verification reflex. Research has shown us that under stress, even highly trained and experienced people will put their finger on the trigger, sometimes with surprising force, when they shouldn't. It's thought that, at a deep level under stress, the brain wants to make sure your finger can find that trigger.
The key here is to train, train, train to keep that trigger finger away from the trigger unless you're intentionally firing a shot. The fact that it's very difficult to do that even with a lot a training suggests that short travel, light weight triggers aren't a good idea in a defensive firearm.
