My own personal Negligent Discharge happened at a gun range on the north side of Houston, years and years ago.
The round went into the dirt a few yards down range.
My finger was on the trigger before I was ready to shoot. That's all there was to it. I placed my finger on the trigger as I brought the gun up onto target, and BANG. Finger came off the trigger, and I stared at the 1911 in my hands with wonder. I had done the same thing with my Glock over and over again.
This is what we call a learning experience. The controls of different firearms are different. It's negligent to ignore this, or to assume otherwise.