How does the study of secondary sources challenge a person’s understanding of history?

Their reliability and validity are open to question, and often they do not provide exact information required by a sociologist.

You get another perspective of the same event, so you can have another person's prospective, not being in the event, and just guessing based on what they've heard, not actually being part of the event.
Hope this helps!
Stay smart,
~{Dunsforhands}