Years ago I spent some time trying to find my relative in the 1840 census, using indexes and manual searches of the county where I thought he was. No luck.
Then I went back and searched for his 1830 neighbors in the 1840 census and looked very closely at the other names on the pages where they were listed in 1840. There was a name that was his--written in a way that was difficult to read with a name that was spelled incorrectly. I'd probably seen it before, but until I knew that I was in "his neighborhood" I didn't look at the entry as closely as I should have.