What was 3M scientist Spencer Silver originally trying to create when he accidentally discovered the adhesive used in Post-it Notes?

Many of today's most successful products weren't actually designed for their eventual purpose. Some of the world's most beloved inventions came about through failed experiments, accidents, or unexpected discoveries. Post-it Notes are a perfect example of corporate serendipity that transformed into a billion-dollar product. Test your knowledge about how this everyday office essential came to be!

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A super-strong adhesive that would bond permanently
A temporary bookmark for hymnals that wouldn't damage pages
A heat-resistant coating for aerospace applications
A waterproof adhesive for underwater construction