Ancestors Keeping a Low Profile
"If you hit a brick wall trying to trace one ancestor," advises Winston De Ville, "forget about that one for a while and concentrate on another lineage." He adds:
But let’s face facts. Some ancestors will prove to be so elusive they may never be found. If records exist, a good genealogist should be able to find them, no matter the obstacles, but even the best researcher cannot find what is no longer there or perhaps never existed. The genealogist’s mission is to exhaust all sources.
See De Ville’s "Some Lineages Can’t Be Traced."