Genealogists deal with information—gathering, analyzing, transmitting and preserving. Often that information isn’t in an easy to use form. Maybe it’s in a foreign language written in Gothic script. The ink has faded. The words are abbreviated and just for fun let’s say it uses an outdated calendar and archaic place names. The meaning you give to that document will depend on many things.
Relativity
How are you connected to the document? Is it a will that lists your ancestor as an heir or a witness? Is the date on the document later than any other evidence that you have about that ancestor? Then a meaning you can assign to it, is that your ancestor’s death date was after the date on the will. You can also conclude that your ancestor knew the author of the will. If your ancestor was the author of the will your connection will be very different. Your ancestor died between the date of writing and the date of probate. You might read about many people who knew your ancestor and get at least some idea of your ancestors possessions. The meaning you give to a document depends on how it fits into your research.
Knowledge
The meaning you assign to a document depends on what you know or what you think you know. Maybe you understand how the document connects to your ancestor but only later do you manage to read a particularly difficult passage, or learn where a certain place was, or that another person mentioned in the document was a relative. Suddenly the meaning you assign that document can change dramatically. What the document means to you depends on what you know.
Ability
The meaning you give to a document will also depend on your abilities. Can you read the language well enough to do more than pulling out what looks like a birth date? Are you able to interpret a document’s archaic language? Even if the answers to those questions are both “yes” right now, were they “yes” when you decided what the document means or have things changed. Would you be able to assign new meaning now with some improved ability?
Intent
Normally we don’t think about a document’s meaning changing. The document was created with a specific intent and that can’t change after its creation. We assume that the intent is the same as the meaning but the intent is only what the document meant to the person who created it at the time it was created. What that document means to us, different people at different times and in different places, is, not surprisingly, different. If we stick to only drawing conclusions from a document that match the original intent, then we may be missing some very important things.