Trapped in your own skin

The advantage that you gain by separating mechanic from skin is that you can shuck off video game conventions and free yourself to develop anything you want. If you think, "I'd like to create a space-themed strategy game", and you think back to all of the space-themed strategy games that you've played, you might think of 4X games like Alpha Centauri or Master of Orion—they both pit you in a massive quest to conquer the universe. They are huge games that you likely won't finish alone. So, you start trimming them down for sanity's sake—"I'll just build Master of Orion with fewer planets," or "I'll just build Alpha Centauri with fewer features." Now you've unwittingly fallen into that self-defeating trap. Your project is still too huge. You eventually abandon all hope. A few years later, you're an accountant wondering what might have been.