1940: Ballpoint Pen.

They’re everywhere now, but it  took years for the ballpoint to make it into the mainstream. Getting the ink right was difficult. It was always too thick or too thin. And if you weren’t holding the pen point-down, the ink wouldn’t flow at all.

Plus, the early pens cost more than $10 each. Then along came Bic, with a pen that worked and cost only 29 cents. Its 1959 ad campaign headlined “Writes First Time Every Time!”  pushed pens into the mainstream. The price soon dropped to 10 cents, and it was good-bye for good to the fountain pen in schools.