Because I use a peppermill to grind my peppercorns freshly, I am unlikely to add too much pepper by mistake.
But I do remember once as a child (maybe 10 years old, or so), when mum used to buy ground pepper and put it into a pepper shaker, the holes in the top of the shaker were blocked, so I took the top off and tried blowing the caked pepper out of the holes. What happened was that the pepper, instead of doing what it was supposed to do, decided to blow backwards into my face (and eyes). I think it took about ten minutes for my eyes to be able to see again. Actually, I thought I had permanently blinded myself.