Apollo’s successful computing software programmer, Margaret Hamilton was one of the reasons why the astronauts came home safely.
One day, Margaret Hamilton 4-year-old daughter, Lauren, was playing with the simulator's display and keyboard until an error message appeared. Lauren crashed the system by launching a program called P01 while the simulator was in midflight.
There was no reason as to why an astronaut would do this, but regardless, Hamilton wanted to add code to prevent this crash from happening in space.
NASA disagreed with this idea, believing that the astronauts would not make any mistakes for they were trained to be perfect. So instead of adding code, she created a program-note that said: "Do not select P01 during the flight".
But five days into the flight, astronaut Jim Lovell selected P01 mid-space. This wiped out all the navigation data! Without the data, the Apollo computer wouldn't be able to figure out how to get the astronauts home.
Hamilton knew this was a possibility so she had a plan devised. Back then, programming meant punching holes in stacks of cards. This would have been processed overnight in batches. But she did it! In 9 hours she uploaded new navigational data and thanks to her, the astronauts came home safely.