Sounds like others have similar solutions.

Often, a construction step doesn't go well. Rather than forcing it, I move on to another piece or even another model. Or I just re-organize the workshop. Generally when I leave it for a while an alternate approach comes to me and I end up modifying something for the better and the enthusiasm comes back.

In any case, taking another model out to burn a few holes in the sky is the cure for frustration I can think of. Not always an option where I live in the great white north so I've started building indoor models....