Yes, sometimes you just have to let a brick wall be. I have one that I've done all I can to break down (including posting on Rootschat) with no result. He had a common name and lived in London. He went bankrupt and disappeared from his family, never to be sighted again. It was almost 30 years before his wife described herself as a widow. I've bought several death certs which seemed possible, but none of them are him. The trail went cold, and though I continue to keep an eye out for him and put his name into various sites, I suspect that unless something unexpected turns up, I will not find him.