You raise some good points about other things that can happen in planning, and your point about opacity in plans along with learning new skills is also something I hadn't considered.

The general idea of "getting things done" doesn't seem to vary, but there's definitely much more room for variation than I've implied.

I think a large part of that is caused by my: 1) Inexperience with applying planning skills 2) Using them only on a very narrow range 3) Extrapolating from my personal experience.