It doesn't. It never is. It can't be.
My favorite example of this was the Moon shot. Each step was learning how to do just that one step. Mercury was just about getting into orbit, not easy even now with SpaceX though they are standing on the shoulders of those giants. Then Gemini for multiple people and orbital maneuvering (that experience gained them lots of learning) and then Apollo 8 was still a dress rehearsal even though they flew around the Moon.
Each step HAD to be simple because complexity weighed too much. But each of those simple steps were still wildly complex.
Every time I would dive in and code up something that I though was easy, it would blow up in some weird way, and I have found that doing each step individually and getting it right, might sound like I was going really slow, but it was smoother so it was faster in the end because I wasn't chasing bugs in all the places, but just one.