More than meets the eye.
Schnowzer and Scribble,
Given the right circumstances we might all be capable of catching garbage numbers. That is, no other ongoing tasks and with no disturbances. I have it, on good authority, that the period leading up to departure in MEL was very busy and presented several disturbances.
Now, I have been in the business for years now and I have seen my share of well managed departure processes. And I have also seen my share of poorly managed departure processes. The point is that it can happen to any one of us, given the right(wrong) circumstances. Just praise yourself lucky that its not your departure thats being investigated.
The challenge, of course, is to come up with the perfect and foolproof way of the operating airplanes. Personally I find that an unachieveable goal as humans are not perfect and we are the ones designing and building airplanes.