I think, in a way, it is about leaving room for ‘failure’. Except, what people regard as ‘failure’ is actually just a different type of success.
Yes, you might not complete (in my students’ case) the (computer) program, with all the requirements met, but you have done these key parts. That is a good thing, and something to build on later. Oh, you didn’t do any of it because you thought the whole thing looked scary? Well, it would have been better to try, but at least you are in a position to learn that – to learn that taking small bites out of the problem, and then seeing what your new roadmap looks like would be a success in and of itself.