X: Dear Y: I have a question for you. Do you ever desire squiggly?
Y: Desire what?
X: A squiggly.
Y: What in the world is a squiggly?
X: It's like nothing you've ever experienced before.
Y: Okay, but what is a squiggly like? Is it an animal? A plant? An inanimate thing?
X: It's like nothing you've ever seen before or experienced before, so I can't give you anything that will give you even the faintest idea of what a squiggly is.
Y: Okay, I can answer your question. I've never desired a squiggly because I have no idea what it is. What do squigglies do?
Y: Do they have parts?
X: They have squacks and squales, which allow them to squiggle, but squacks are nothing like anything you've seen in your life, so too squales, not to mention squiggling.
Y: I have no idea what you are talking about. I can tell you with absolute certainty that I have never nor will I ever desire a squiggly. I don't know if it is food that you are talking about, an animal, a pet, a flower, etc. So no, I have never desired a squiggly.
X: You are closed minded.
Y: Why?
X: Because you said you'd never desire a squiggly. How do you know that?
Y: Because I can't desire what I do not know.
X: Sure you can. Did you not desire to fly with Peter Pan and go to Neverland when you were a kid?
Y: Yes, I did.
X: There you go! You can desire what does not exist and what you've never known to exist.
Y: Not quite. I know what flying means, I've seen birds fly, I know what "land" is, what a "foreign land" is, I know what "playing" is, and I know what a life without responsibilities and worries is (it was the life I had when I was 4). Peter Pan is just an imaginary combination of all these factors and more that I know about and have experienced already, and so I can desire to fly like Peter Pan, I've been in an airplane before, I have jumped off a diving board before, I have been up high in a skyscraper before, and I swam in deep water before, so I can take all those experiences, put them together in my imagination in a different configuration and order that they have in reality, and I can get a sense of what it would be like to fly. It would be like swimming in the water, but without water, and high up in the sky, with a much better view than I'd get in a pool. And I've been to an amusement park before, so I know what it would be like to be in a place that is fun and exciting, etc. And so I can desire to go to Neverland, but that does not mean this desire does not follow upon knowledge of some kind. A number of things exist that I have experienced, and together this manifold of experiences enables me to desire the product of a writer's imagination (namely, the world of Peter Pan). It's the same thing with wanting to go to Narnia, or Middle Earth, or outer space, etc. So I cannot desire what I do not know, only what I know.
Desire always follows upon knowledge; and so whatever we desire, that motion is preceded by a knowledge of some kind. If you and I desire a happiness that is complete, sufficient unto itself (which means that it is not subject to the contingencies of concrete existence that can eliminate that happiness, i.e., a stock market crash, a sudden disease, bad weather, etc.), and enduring, unending, or eternal, etc., then at some level I must know that which gives rise to such desire. And as we go on in life, we continue to seek this happiness, this complete and enduring and self-sufficient happiness, but everything lets us down, that is, nothing answers to it. Everything we experience is good to a degree (a finite degree), but nothing brings complete rest to our will (the human heart); we still seek a happiness that is complete, eternal, and non-contingent. What we ultimately desire is God, who alone answers to that desire, for to be God is to be eternal, non-contingent, complete, the source of all that is good, hence Goodness Itself. We have a natural but confused knowledge of God (a preconscious knowledge); if we did not, we would not desire what is enduring, complete, and sufficient unto itself. At some preconscious level, the human person desires God, and some people explicitly recognize this and do not confuse God with money, honors, or anything else; others, on the contrary, do not explicitly realize this and pursue what they think will bring them complete rest, namely money, good weather, travel, a life of ease, etc. The only problem is that it fails in the end; such people continue to want more, continue to search, and they cannot hide from the fact that their life is precarious and subject to bad luck, to disease, destruction, old age, etc., so they know that no matter what they possess in this life, it is temporary. An explicit religious sense is an awareness that what I want above all things is the totally "other" and supremely good and beautiful, and source of all that is good and beautiful, namely God Himself.