The invention nobody knew what to do with

In 1968, Spencer Silver, a chemist at 3M, was trying to create a super-strong adhesive and got the exact opposite: a weak glue that peeled off cleanly and could be reused. For years he pitched it all over the company and nobody saw the point. It was, people said, a solution looking for a problem.

The problem belonged to Art Fry, another 3M engineer who sang in his church choir and kept losing the bookmarks in his hymnal. In 1974 he remembered Silver's adhesive and made markers that stuck and unstuck without damaging the paper.

The first launch, in 1977, flopped; the 1980 relaunch, backed by mountains of free samples, was a smash. And the canary yellow? Pure chance: it was the colour of the scrap paper lying around in the lab next door. Even that was an accident.