You don't wear it out. You land the head long of your aim point, and splinter the handle on whatever you were trying to hit. It's certainly not hard to ruin a handle if you're learning to swing a sledge by driving steel splitting wedges.

There's a huge difference between say, weilding a hatchet on a camping trip, and trying to get the hang of a splitting axe, with a 3ft or longer handle, when you're a kid. Getting a long, sweeping arc that comes down in the right spot isn't easy and if the axe head's centrifugal force pulls it away from you, you clunk the handle down on the wood. I definitely recall my hands ringing and numb from those kinds of impact. I don't remember ruining a handle, but if it had been my chore, I think I could've come close.