What was the original 'failed' product development that eventually led to the invention of Post-it Notes?

Product innovation often comes from unexpected places! In the world of inventions and discoveries, some of the most successful products emerged from failures or accidents in the development process. The story behind the creation of Post-it Notes represents one of the most fascinating cases of accidental product innovation that transformed into a global success. Test your knowledge about this iconic product's journey from laboratory mistake to office essential.

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A super-strong adhesive that accidentally turned out to be removable
A waterproof paper that unexpectedly could hold small amounts of adhesive
A heat-resistant bookmark that could withstand high temperatures in industrial printers
A color-changing paper intended for thermal receipt printers