Ah, you added the beginning:

Here is my secret. It is very simple : It is only with the heart that one can see rightly. What is essential is invisible to the eye. ~The Little Prince

Your heart is worth wearing on your sleeve...

It's, to me, I think such an impacting and meaningful quote. St-Exupery, in his short 44 years, surely was a philosopher and wordsmith. The Little Prince, both as a young student learning French, and then again reading it in English -- among his other brilliant words -- to this day, is one of the deepest books I've ever read.

Also, about wearable hearts... I liked this as a teenager:

"My heart is yours to fill or burst,

To break or bury,

Or wear as jewellery,

Whichever you prefer. "

I guess of those options fill is best? :)

What makes The Little Prince so profound?

Fill is definitely best. :) A girl who liked me used to quote that song to me. #nostalgia

The Little Prince is like all great parables, teachings, or stories; it can be enjoyed at many levels.

At the surface level, it is an incredibly silly story. Elephants. Kings. Planets. Roses. Foxes.

When I first read it -- perhaps because it was in French and perhaps because I was 14 -- I sincerely thought it was a wild fantastical children's book, almost similar to the movie "All Dogs Go To Heaven," which, when watching it later as an adult, just seems absurd. Like someone wrote it when they were under the influence...

But as one goes deeper into The Little Prince, the little prince goes deeper into one; love, children becoming adults, adults becoming children, relationships -- with others, with ourselves.

To this day, I'm not sure I can explain the book other than that while there are many great quotes, the whole is definitely much, much greater than the sum of its parts and it must be consumed in its entirety to view the world as the little prince...as the narrator...as the St. Exupery does.

But that's not simple, so maybe I don't understand it. Perhaps I should try again and make it simple:

The Little Prince teaches us about finding and losing and letting go, and finding once again. It is about never forgetting to draw our sheep, tame our rose, or play with our fox -- to never lose sight of the things that are most important in life.

After all, what is truly essential is invisible to the eye. It is, of course the great secret of humanity: it is only with the heart that one truly sees.

Is this similar to "the best things in life are free" or "stop and smell the roses"?

Or is it closer to "if you love someone, set her or him free"?

I think it's something like, stop and talk to the rose, for even though the are hundreds, once you learn her name, she'll always be your special rose among thousands. :)