When evaluating past eras, historians depend on primary documents and other resources to understand events and cultures. For instance, it would be difficult to evaluate why people once thought Earth was at the center of the solar system unless you analyzed documents from the time in which the idea was relevant.

What difficulties do you think might arise when trying to understand ideas from the past, especially when those ideas are so different from our modern thinking? Do you think primary resources show a complete picture of the period they are from? Give an example or two to illustrate your answer.