"Full many a gem of purest ray serene The dark unfathomed caves of ocean bear: Full many a flower is born to blush unseen And waste its sweetness on … - Thomas Gray

"Full many a gem of purest ray serene
The dark unfathomed caves of ocean bear:
Full many a flower is born to blush unseen
And waste its sweetness on the desert air"

A good many flowers bloom and fade away in deserted places, seen by no one.
In its context in Thomas Gray's "Elegy" it is actually a metaphor for common folk who do heroic things that are never reported in the news or recorded in history. Like a precious stone unmined at the bottom of the ocean or a beautiful flower blooming in the deep woods, their work may not be seen or known, but it is nevertheless heroic. Rubies and roses are beautiful, Gray would say, whether anyone ever sees them or not.