Persistence is a must. You will hit your brick wall and may be stuck for years. Keep at it. You may need to set it aside for a time, but after a break return to the search and look at it fresh.

Is there a new angle or approach you haven’t tried?

There are lots of genealogy bloggers who write about such things, seek out their ideas. There are also books on the subject.

You may not be the one to break down the wall. If that’s the case, document your efforts so that whoever inherits your work can pick up and be the one to make the breakthrough.