Walter Hunt had no trouble thinking up new ideas. First he invented a machine to spin flax. Then he invented a fire engine gong, a forest saw, a stove that burned hard coal. His inventions worked, but he just did not have the knack for making money from them. One day in 1849 Walter Hunt wanted to pay a fifteen-dollar debt to a friend. So he decided to invent something new.
From a piece of brass wire about eight inches long, coiled at the center and shielded at one end, he made the first safety pin. He took out a patent on his invention, sold the rights to it [to his friend] for four hundred dollars, paid his friend back and had three hundred eighty-five dollars to spare.
Then he watched his latest brainstorm go on to become a million dollar money earner for someone else.
From Why Didn't I Think of That by "Webb Garrison";
I couldn't possibly have said it better