In 1849 Walter Hunt owed someone fifteen dollars, and the story goes that he sat down with a length of wire to invent his way out of it. What he twisted had a coil at one end to make it spring and a clasp at the other to hide the point: the safety pin, patented that April and sold outright for $400. He paid the debt, kept the rest, and never saw another cent from a thing that now lives in nearly every drawer. In the 1830s he had built one of the first sewing machines to make a lockstitch, and by most accounts he chose not to patent it, worried it would put seamstresses out of work. So the invention he let go for almost nothing was the one he made for money, and the one he left on the table, he left there on purpose.