If your inner motivation is satisfying intellectual interest or improving skills, you actually finished the real project behind the facade without a need for finishing the official project.
So, the mistake boils down to making up a fake official project as kind of a justification for satisfying your real needs. Maybe you would feel better if you are true to yourself and say "I do this to explore and learn, I don't actually ever intend to deliver a presentable product with this activity.".
This. I felt much better once I realized it and learned to 'delete' projects. These are like sketches an artist makes to practice for the real thing, which often never comes. But it is a satisfying learning experience.
Working backwards from the end result is a good practice to see where you want to take it. And the end result is not the deliverable itself, but how, for what purpose and by whom it is used. Will you want to charge money? Do you offer it for free to anyone? Will you take feedback? Does it solve a personal problem? If you can't answer these kind of questions, then maybe it really is the journey and you never intend on finishing a product anyway, which is fine.
So, the mistake boils down to making up a fake official project as kind of a justification for satisfying your real needs. Maybe you would feel better if you are true to yourself and say "I do this to explore and learn, I don't actually ever intend to deliver a presentable product with this activity.".