Post-It notes were invented by Dr.
Spence Silver, working at the research facility of
3M. Silver was looking for a way to improve the strength of
acrylate adhesives. But the experiment failed; what he found was an adhesive that worked rather poorly.
Instead of tossing out the failed product, Silver found a brilliant way to use the glue. Attached to a a piece of paper, it made an excellent bookmark that would stick and remove without damaging the book.
By coincidence, Silver used one of his bookmarks to pass on some written information to his manager. When his manager returned the bookmark, they realized that they had just invented an interesting new product.