Answer:
The correct answer to this open question is the following.
The difficulties I think might arise when trying to understand ideas from the past, especially when those ideas are so different from our modern thinking are that people cannot understand the circumstances that were present in past events in order to understand the meaning of those events. If we want to understand how and why things happened in the past without knowing those circumstances, then our view would be biased or incomplete. Primary resources show a complete picture of the period they are from but in a partial way. You have to connect the dots, the stories of that time in the past to have the full perspective of the events.
The example would be the following. If you try to understand the reasons that led to the American Civil War just from the perspective of the southern states, your information would be biased. You have to know both sides of the story to have the full view. Again, understand the circumstances will help you to get the right idea.