Perfection is an unattainable illusion. No one gets it right all the time, and that includes air traffic controllers. We certainly try, given the safety stakes at play in our job. Human nature, however, has other ideas.
There could be any number of causes for an oversight. Maybe a controller’s just been plugged in too long on a busy day, getting his head kicked in by nonstop, complex traffic. Short staffing means there’s no break anywhere on the horizon. Oh, and he’s got to pee. I’ve been that guy. It’s not fun being tired, distracted, and inundated with airplanes.
