From lab mistakes to fortunate fumbles, some of humanity's most crucial lifesaving inventions were never meant to happen. We're counting down five accidental discoveries—including a moldy petri dish and a failed sweetener experiment—that transformed medicine and safety forever. These happy accidents have collectively saved more lives than most intentional inventions combined.

In 1909, Fritz Haber and Carl Bosch cracked one of chemistry's greatest challenges: pulling nitrogen from the air to make fertilizer. This single invention now feeds nearly half the world's population, but it also armed both sides of two world wars and forever altered Earth's nitrogen cycle.