In 1979, a passenger jet carrying 250 people left New Zealand for a sightseeing tour to Antarctica. Unknown to the pilots, their flight coordinates were off slightly, just one degree. A small error, but it put them nearly 30 miles off course by the time they reached Antarctica. Before the pilots could correct the mistake, the plane crashed into Mount Erebus killing everyone on board.
Small mistakes accumulate over time. If something is off course by just one degree, after one foot, it will miss its target by an eighth of an inch.