Another modern invention we owe to a happy accident is Post-it Notes,those small pieces of notepaper that can be stuck and unstuck again and again.In 1970,Spencer Silver was working in a research laboratory,trying to create a strong adhesive.He created a new adhesive that stuck to objects,but it could also easily be lifted off them.Because the adhesive was so weak,Silver considered it a failure.He shouldn't have.A few years later,a co-worker of Silver's was singing in a choir.He used scraps of paper to keep his place in the song book,but the scraps kept falling out.Remembering Silver's invention,the co-worker put some of the adhesive on the scrap.It was perfect! The scraps stayed in place,but came off easily so they didn't damage the book.Post-it Notes were introduced in 1980,and quickly became and essential office product around the world.