Post-it Notes are ubiquitous today, but before their invention in 1968, no one knew what they were missing. It was that year that Spencer Silver, a chemist for 3M, was hard at work trying to develop a strong, tough adhesive. What he came up with was nothing of the sort, but had a usefulness all its own: microspheres, which are microscopic bubbles of adhesive that maintain their stickiness but can be removed easily without damaging a surface. Silver knew he had something innovative on his hands, but couldn’t find a use for it. That is, until his colleague Art Fry found one. Every Wednesday night at choir practice, Fry would use scraps of paper to mark the hymns they planned to sing at the upcoming church service. By Sunday morning, many of the scraps would have fallen out of the hymnal. Fry remembered the invention Silver had been touting, and he realized the microspheres could be used to create adhesive, non-damaging bookmarks. The two men partnered to create the new adhesive sheets and soon began writing messages on them to each other. “I thought, what we have here isn’t just a bookmark,” said Fry, according to the brand’s website, “It’s a whole new way to communicate.” With that, an essential office tool was born.