Potato chips. In the 1800s in New York, a customer at a restaurant sent back French fries because they were too thick. The cook made thinner ones that the customer still thought were too thick. Exasperated, the chef made ones that were exceedingly thin to piss off the customer... who loved them.
The Slinky toy was the result of a failed attempt by engineer Richard James to produce an anti-vibration device for ship instruments. His goal was to develop a spring that would instantaneously counterbalance the wave motion that rocks a ship at sea. Instead, he developed the Slinky.
The Kleenex tissue was originally designed to be a gas mask filter. It was developed at the beginning of the First World War to replace cotton, which was then in short supply as a surgical dressing.
The x-ray was discovered purely by accident. When German physicist Wilhelm Conrad Rontgen was experimenting with cathode rays in 1895, he put an activated Crookes tube in a book and went out to lunch. When he returned, he discovered that a key that had also been placed in the book showed up as an image on the developed film!
Finally, while attempting to develop a super-strong glue, 3M employee Spencer Silver accidentally developed a glue that was so weak it would barely hold two pieces of paper together. However, his colleague Art Fry needed the glue. Fry sang with his church choir and marked the pages of his hymnal with small scraps of paper that often fell out. He used Silver’s glue to hold the papers in place. Today we call this invention Post-it Notes.
The microwave oven. Shortly after the Second World War, Percy Spencer, an employee at Raytheon, walked past a microwave emitter which was being developed for military purposes, and noticed the candy in his pocket melting. Apparently, other Raytheon employees had noticed this phenomenon but they had all ignored it. Raytheon produced the first commercial microwave oven in 1946.
Nobody has mentioned Viagra, also known as Sildenafil. It was originally created to treat high blood pressure, but during the failed clinical trials, it was noticed that the medication was very effective at causing erections.
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