I bet if you were someone who could make a hammer that would have been a good stable job for years, centuries even. Almost everyone needs a hammer at some point in their life.

“Hey, where’d you get that hammer?”
“Oh, you gotta talk to Bartholomew.”

Then some guy, Greg, would see how busy the hammersmith is making hammers one at-a-time and say, “I’m going to make hammers one hundred at a time!” He’d pay Bartholomew not to make him one hammer, but to make a mold that could make one hundred hammers at a time. Greg has rich parents, he can afford this sort of risky business venture. One hundred hammers for the price of ten, that’s profit.

After the hammer mold, Bartholomew would still get paid. No one actually likes pouring molten iron and hammering, but Bartholomew doesn’t mind. He’s making less money per hammer, but he’s also producing more hammers with a lot less effort, so it nets out okay. The job is less interesting – making hammers and nothing else – but he didn’t like being a salesman and dealing with wayward customer requests anyways. There’s lots of money in churning out hammers this way, it’s more efficient and people like Greg love selling them and making money. Bartholomew buys himself a new ox cart.

Then some other guy, Jeff, seeing all those hammers and all that money, would say “I’m going to make a machine that makes a million hammers a day.” Jeff knows a regional lord who is friends with the king and has big treasure chests. He’d hire Bartholomew and his hammersmith friends to build a giant complex machine with whistles and gauges and a furnace that makes ten hammers a second. A million hammers a day for the price of a thousand hammers, now that’s profit!

The profit charts are going up. Hammers are about as cheap as possible to mass produce… except now Bartholomew and his hammersmith friends are starting to catch the ire of bookkeepers. They’re starting to look expensive compared to the penny hammers that sell for $10. They fire Bartholomew. He’s given three months of pay, which is nice, but in exchange he has to sign a contract saying he’ll never make another hammer machine again in his life. Hopefully Bartholomew squirreled away enough money to retire with dignity, otherwise what’s an old hammersmith do when there’s no more hammers to make?