He grabbed the wrong part and saved millions

In 1956, the American engineer Wilson Greatbatch was building a circuit to record heart sounds. Reaching for a resistor, he dipped into the wrong box: he installed a one-megohm part where a ten-kilohm one should have gone. Instead of recording pulses, the device began emitting them, at a rhythm astonishingly close to a human heartbeat.

Greatbatch instantly understood what he was looking at: a pocket-sized artificial heartbeat. He spent two years shrinking the circuit until it could be implanted, and in 1958, working with surgeon William Chardack, he got it to pace a dog's heart. The first human patients followed in 1960.

Not content with that, he later invented the lithium-iodide battery that still powers many pacemakers. Millions of people are alive today because one day, somebody reached into the wrong box.