First, we do not even realize a skill is difficult. "I could do it too!" we think. That stage is called "unconscious incompetence". We try it, then we realise: not so easy as we believed!
Second stage arrive: "will I ever be able to do it?" Called Conscious Incompetence in the Learning Systems Manuals and articles. At that stage we need to be given confidence that yes, with practice and thinking about how and what we do, skills can be learned.
Third stage we begin to realize: "Yes! I arrived! I can do it!" Conscious Competence arrived, but we still have to think while doing it, practice and think, practice and think.
Finally, arrives a stage when we do without needing to think about it, freed to think or do something else at the same time. The stages are not so clear and net and, we arrive all the time to a new stage a new level when we add something new to what we knew.
Till we did not arrive to the top of one pair of stairs, we can not see what is after the next corner. The horizon opens up, once we are up, only then we can see farther ahead.
The path and the levels were carefully designed by educational experts, knowing this and a lot more. I am reading a book that explains so much about the "why" the path, levels and projects are as we have them now. With time, I will try to describe them here.