Topix Underground

"After Neil Armstrong and Buzz Aldrin landed on the Moon, they prepared to lift off and return to the Command Module. When they went to arm the ascent engine, they discovered that a circuit breaker switch had broken off (it was probably knocked loose when Armstrong was moving around in the cramped Lunar Module).
Without that switch, they couldn’t fire the engine to leave the Moon. They would have been stranded.
Buzz Aldrin took a ballpoint pen and used it to push the broken circuit breaker into the “on” position. It worked. They were able to arm the engine and lift off safely from the lunar surface.

— a humble ballpoint pen literally saved their lives. Without it, they would have slowly died on the Moon after their oxygen ran out."