My brother and I have both taught at the college level for years. After dealing with so many students, one fact is more than apparent to both of us; most students' knowledge of history is abysmally poor. History, as such, is no longer taught in many high schools or grade schools. Now, the children have classes in "social studies." Which is a euphemism for whatever popular social activist philosophy is current at the time.
I remember my own history classes in high school and grade school and it seemed that we never got past the U.S. Civil War by the end of the year. Even after taking classes that "covered" the Civil War, I can remember when, later in life, I read a number of books about the War to be surprised at what happened. My school classes never really explained the War in sufficient detail for me to understand what had actually happened.
Now, what does this have to do with genealogy? Everything. Given a particular date and place, can you tell what was happening in that township or county at the time? Unless you have made a particular effort to do so, it is unlikely that your general knowledge of history supplies any clues. As a result, as I have found in my own family, people make incredible errors in time and place.
In one example, one of my Great-great (back a ways) Grandfathers was supposedly born in the Salt Lake Valley in 1795! (Just in case that doesn't mean anything to you, the pioneers didn't reach Utah until 1847). I find this kind of error all the time. But there is a more significant problem. That is, assuming that just because you have a date and a place, you are finished with the story and the research.
I have talked to dozens (probably hundreds) of people who express the idea that they have reached a "brick wall." In almost every single case, (there are exceptions and you, the reader, are probably one of them) the person turns out to know almost nothing about the local history where they are looking. Most fishermen know more about the fish and the lake bottom than genealogists know about the history of the local areas they research.
This post is not aimed at the meticulous historian/genealogists who know all about their ancestor's personal lives and history. It is aimed at the vast majority, who never bother to read a history book or check to see if one exists.
By the way, pick a county in the U.S. Now go to Google Books and look for a county history. What did you find? Have you read the book or at least looked at it? Here is an example: