Last week we had the monthly meeting of the local U3A (University of the Third Age) Genealogy Group, and several of the queries were ones which might have been answered if the questioner had taken a better look at the document containing a reference to their ancestor.
In one case it related to the identity of the witnesses to a couple of marriages a generation apart. What can happen is that many marriages may have been witnessed by the church wardens - rather than by relatives or friends of the couple. It is therefore worth looking at adjacent marriages in the same register - and if the same witness names keep turning up they were probable not relatives of any of the couples.
Another similar problem can occur if your ancestor has a puzzling occupation. In some cases he did a specialist job in a local industry - and the occupations of others living in the same street will jelp to identify the industry - and hence lead to an understanding of what your ancestor did. (For instance I have come across a "rag sorter" in an area where many neighbours worked in the paper making industry.)
On other occasions a large family in a small house may "lend" some children to the less crowded house next door - or perhaps your ancestor married a girl from the same street.
It is very easy for beginners to metaphorically rip their ancestors names from old records without realising that there may be other clues to who their ancestors were, and what they did, in the same documents,