Why is something or someone deemed unimportant referred to as being “just a footnote” when footnotes tend to refer to significant earlier works that support an argument?

Question

Why is something or someone deemed unimportant referred to as being “just a footnote” when footnotes tend to refer to significant earlier works that support an argument?

In: Culture

Answer 1

Because while the footnote might be important, it wasn’t important enough to get included in the main text.

Basically “something or someone, just a footnote” might be important to a portion of the story, but they aren’t a critical/crucial part of the whole story.