Reframing an extract as a quotation constitutes a kind of coauthorship. With no change in wording, the cited passage becomes different. I imagine that the thrill of making an anthology includes the opportunity to become such a coauthor.

Some lines are born quotations, some are made quotations, and some have "quotation" thrust upon them.

Not everything that can be extracted appears in anthologies of quotations, in commonplace books, or on the back of Celestial Seasonings boxes. Only certain sorts of extracts become quotations.

I wonder if "an" ever occurs before "haughty" except in a quotation, or whether you can make anything sound like a quotation by adding a word like "goeth"?

The attribution of a speaker is in fact a part of the quotation. Some statements simply are better if a certain famous person said them.

A single gnomic line can come to resonate with centuries of subsequent wisdom.

We sometimes think of quotations as extracts from larger texts, but some quotations originated complete unto themselves.