1. This circle represents the source you have.
This circle represents everything there is to know about a topic.
This circle represents the source you have.
You need to judge how much of the topic the source is showing you.

2. All knowledge Source This source....
...misses out this bit of the story.
...tells me this bit of the story.
Source
...tells me this bit which isn't relevant to the story.

3. All knowledge
This source....
...misses out this bit of the story.
Source
...tells me this bit of the story.
This source is more complete.