Too Much Force
When I was little, my mother and I were gardening. I asked her what the knob in the middle of the shears did. When she didn’t answer, I turned it in any way. The shears didn’t seem to change in any noticeable way until I tried to close them and I found out that it was to make the blades easier or harder to open.
I put in the usual amount of force I needed to close them, but it was now drastically too much. I closed them so quickly that I lost control and they cut my upper lip in half. It’s a cool scar. Story credit: Reddit/Aidan_cba