One of many problems that family historians and genealogists encounter is trying to sway other researchers that an error has been made in previous research or that previous research has been misinterpreted.
This may be due to several factors:
 Family lore that folks just won't let go of, no matter what evidence disproves the story.
 Transcription errors in records. Often numbers are misread in dates [3 for 8, 1 for 7, etc.]. Dates are copied incorrectly from one source to another. Numbers are transposed [84 become 48]. A name is misinterpreted [John for Jonathan, William for Willard, etc.] An incorrect word or misspelling.
Punctuation, or the lack thereof, in a document can also lead to mistakes.
 Language barriers. A clerk writing a name in a marriage record, deed or some other document, could misunderstand the person giving them the information. [dialect, regional accent come into play.] This could result in a misspelling of a place or name. Literacy and freelance spelling come into play here as well. If you can't read or write, there's a good chance you won't be able to tell the clerk how your name is spelled. The clerk wings it. Cochran becomes Corcoran, Cockrun, Coccrin, etc.
 Misinterpreting evidence. If the researcher does not pay close enough attention to relationships, family naming patterns and similar factors, the results could have children ending up in the wrong family. The assignment of children to parents in early genealogies was sometimes guesswork. The evidence may have been there, but was not followed closely enough.
 New research supplants earlier research. This ties back into #1 above. It is often hard to change minds. In some cases the new research is somewhat theoretical, not clearly supplanting the older research. Other times it involves new evidence that clearly changes the picture.
 Geographical errors can be a problem. There are two couples named, say, James and Sarah Neal residing in two different counties in the same state/colony. You have ancestors by the name of James and Sarah Neal living in South County. Their daughter is born in Midd County. You need to make sure that you have the right couple. Was the other Neal couple from Midd or a bordering county?
 Deeds and probate records can lead to major discoveries or add confusion. Everyone named in a deed or will needs to be correctly identified. Punctuation was often lax in wills and other records. That could lead to errors in interpreting the number of children and crucial facts in the document.
I will be examining each of these seven items over the next several posts using personal research for examples.