This hits for to me because I'm currently adding on to my house. Or rather, paying professionals to add on to my house, because I actually want it to get finished.
I visit every couple of days. It's REMARKABLE how fast things get done. One day, there were no walls. The next day, almost all of the walls were in place!
... and yet, at the same time, things take a long amount of time because reality has a surprising amount of detail. I haven't taken into account how much you have to do to frame a house. So incredible amounts of work get done, day after day, but 3/4 of them are things I had no idea needed to get done! Gazing up into the roof, the detail is incredible. The PSL beams, the brackets, the joists, the trusses, just.. EVERYTHING!
I thought the structural engineer's plans had an incredible amount of detail on them, and they do, but they also don't really say anything about _how_ to build the thing. How to put up the walls, how to hold them together temporarily, how to lift beams into place. In what order things can and should be done. That all just takes experience.