Write down everything you think you know about a specific ancestor. Do not refer to anything other than what is in your mind. Include birth, death, marriage information, likely educational level, religion, occupation, how often the person moved, etc.
When you are done, see what pieces of information you can find in actual records or “reliable” sources. Those other pieces of information about your ancestor for which you have no source may not be true, could be partially true, or completely incorrect.
But if you have those pieces of information “in your head” while searching for your ancestor, they could be impacting how you search, what types of records you look for, etc.
And that could be hindering your research.