And another would-be terrorist who was part of this plot decided to just abandon it and head back home because he got bored.

I'm not sure if there's any analysis of the proficiency of the terrorists who flew the planes into the buildings out there, nor how this was determined conclusively, because I haven't done a deep dive into the subject myself.

But what is important to understand is that this paints a picture of how professional, or rather how unprofessional, this operation was.

Other evidence that points in this direction is the movements of Mohammed Atta (and I believe one of his co-conspirators) on September 10th.