What I do at that point is to metaphorically throw everything away and start again from scratch. What is the absolute minimum amount of rules that you can put together to approximate the game experience you want? Slowly add things back in until you get to a minimally playable state. Then you can experiment with adding in some of the other stuff. It may be things you’ve already written, which is why we’ve only metaphorically thrown it away, or more often I find it’s a more elegant version that I wouldn’t have thought of without the ritualistic elimination of previous design.

Or I run away from it and never come back. I’ve had success both ways.