The real story
In 1968, 3M chemist Spencer Silver was trying to make a super-strong adhesive and got the opposite: tiny sticky spheres that held lightly and peeled off clean. He spent years showing it at internal seminars, calling it 'a solution without a problem'. In 1974 his colleague Art Fry, frustrated by bookmarks falling out of his church hymnal, remembered it.
Fry developed the idea in 3M's 'bootlegging' time, the hours staff could spend on their own projects. The first test launch in 1977, as 'Press 'n Peel', flopped because nobody understood it until they tried it. So in 1978 3M flooded Boise, Idaho with free samples, people loved them, and Post-it Notes went national in 1980. The famous canary yellow came from the scrap paper the lab happened to have.
