Information Window

A good documentary is a window - but not necessarily to a different time or place (that's the role of fiction). 

A documentary is a window into a new idea.

And an idea is, basically, a collection of information.

Your job then, as a documentarian, is to create the most interesting & persuasive collection of information about your topic.

Next, narrativizing this information in the most competitively stylish way possible.

Sacrilege

How Walt Disney Films a Lecture