People are only statistically predictable, individually, it is sometimes impossible to guess what they will do or where they might go. Commonly, however, the further you go back into the past doing research, the more predictable people become. In the 1800s it is not unusual to find concentrations of families in relatively small areas but, it is obvious that 20th and 21st Century technology has increased work and transportation opportunities, resulting in greater family dispersal.
My wife and I had dinner with four of our old friends (two couples) and got updated on all of our children's marriages, grandchildren and the places they are now living. For many years we lived next door and across the street from each other. Our children all grew up together and have now all gotten married and moved away. Two of us have moved from the old neighborhood and time has taken it toll. It was interesting to see children as far away as Peru and others living in the next suburban town. All of our children are married and only one family lives close to us. Combined, we have seventeen children and most of them live in other states across the U.S., like Pennsylvania, Florida, Alabama, Texas, North Carolina, Utah, Montana and New Mexico. Who would guess? There is absolutely no way of predicting where these closely associated family members would end up. By the way, combined, we have almost 50 grandchildren.
Even though the general rule in the earlier centuries was that people stayed pretty much in the same area, there were always exceptions. In one case from my family, the husband abandoned his family and disappeared. I finally found him in Northern California with a new family. In another California case, the husband disappeared and I located him in the Census records in a prison. How would you know and how would you guess?
I spent some time looking for an early Utah pioneer who joined the "California Volunteers" and lost contact with his family. The only evidence we had was a letter written from a military fort in Utah after the Civil War. We narrowed down the search to military records still in the National Archives, but he is still lost.
Common names compound the issue of trying to find the elusive moving target but in every case, it is important to anchor the search with an initial location and confirmed name. In at least two cases recently, my friends have admitted that they were looking for relatives with the wrong name for many years. Always remember to move forward a generation or even two and do more thorough research before spending an inordinate amount of time looking directly for the missing person.
One of the most common issues is connecting immigrants to their country of birth. Remember the rule, find the immigrants' origin in the country where they settled. Look for records in the new country. Name changes and poorly transcribed names are often a barrier to identity, but records in the country where the immigrant settled may contain valuable clues. For example, many immigrants transferred their church membership to the new country and the church records may show the name or place of the church they came from.
In more recent times, you may have to avail yourself of detective and skip-trace techniques to find elusive ancestors. Despite the best efforts of some people that wish to remain anonymous, our modern record systems are very inclusive. It is possible for a person to break off all contact with his or her family, change their name and move to an unpredictable location, but those cases are quite rare. Most lost people are merely out of contact and not actively trying to avoid detection. But like my ancestor in California, people do run afoul of the law and end up in jail or prison.
Missing people are like missing pieces of a puzzle. You may have to complete the whole puzzle before the identity of the missing piece becomes obvious.