Spencer Silver & Post-it notes

In 1970, American chemist Spencer Silver created a weak glue while actually attempting to develop a super-strong adhesive for the company 3M. No use could be found for the glue until his friend and churchgoer Arthur Fry began using it to stick a bookmark in his hymnbook. The glue gave him the ability to fix the bookmark for a short period of time before removing it and using it again at a later date. Today, post-it notes are one of the highest-selling stationary items in the world.