Creating things nobody ever have done before is one of the deepest feelings you can feel in this life when you have done that, but also is terrifying emotion while you are doing it.
Like a chemical reaction, for something to be deeply satisfying from an emotional point of view you first need to give the system enough energy for the reaction to happen.
It requires intense focus, that is deciding not to do other things, which is painful. It is slow, which is frustrating. The work that could not be automated is boring. It is very expensive if you hire others to help you, and involve a tremendous risk if after all the work, it doesn't work out.