why should you not hit two hammers together?

Question

I’ve heard that saying countless times and no amount of googling gave me a satisfactory answer.

In: 8838

Answer 1

I tried to use a sledge hammer to drive a wood maul the rest of the way through a log. Felt a sharp zip in my wrist and realized that a dime sized piece of shrapnel went through my arm near my wrist and hit the bone inside. I show kids the scar on my arm and the piece of shrapnel when I talk to them about safety. Needless to say, I don’t do this anymore.