The brake pedal shaft has a hole in it. A pin goes there, and attaches the shaft to a stirrup. The stirrup is part of the master cylinder. The pedal shaft pushes into the Y of this stirrup. A person might think that if that pin falls out, the brakes will still work, pushing against the rod even without a pin.

Except that if the pin falls out, the pedal springs toward you, and disappears up under the dash right behind the steering column. You will reach for the brakes and your foot will find air. No pedal anywhere. You have to tilt your head to one side to even see where it has gone to.

I didn't hit anything, but from now on I will keep an eye on the cotter key that keeps that pin in place. And I squeezed the stirrup together so there's no pressure rubbing against the cotter key.