Thomas Alva Edison was working on the invention of the light bulb for quite some time. One day, after creating a new prototype he called his young assistant to carry the light bulb to the lab for further testing.
The assistant was very nervous about this task. He took the bulb – and dropped it. It smashed into pieces. Prototype lost.
Edison started working on another one of these prototypes and when it was ready for testing, he called the same young boy to bring it into the testing lab.