You may have noticed that the books you really love are bound together by a secret thread. You know very well what is the common quality that makes you love them, though you cannot put it into words: but most of your friends do not see it at all, and often wonder why, liking this, you should also like that. Again, you have stood before some landscape, which seems to embody what you have been looking for all your life; and then turned to the friend at your side who appears to be seeing what you saw - but at the first words a gulf yawns between you, and you realise that this landscape means something totally different to him, that he is pursuing an alien vision and cares nothing for the ineffable suggestion by which you are transported. Even in your hobbies, has there not always been some secret attraction which the others are curiously ignorant of - something, not to be identified with, but always on the verge of breaking through, the smell of cut wood in the workshop or the clapclap of water against the boat’s side? Are not all lifelong friendships born at the moment when at last you meet another human being who has some inkling (but faint and uncertain even in the best) of that something which you were born desiring, and which, beneath the flux of other desires and in all the momentary silences between the louder passions, night and day, year by year, from childhood to old age, you are looking for, watching for, listening for? You have never had it. All the things that have ever deeply possessed your soul have been but hints of it - tantalising glimpses, promises never quite fulfilled, echoes that died away just as they caught your ear. But if it should really become manifest - if there ever came an echo that did not die away but swelled into the sound itself you would know it. Beyond all possibility of doubt you would say “Here at last is the thing I was made for.” We cannot tell each other about it. It is the secret signature of each soul, the incommunicable and unappeasable want, the thing we desired before we met our wives or made our friends or chose our work, and which we shall still desire on our deathbeds, when the mind no longer knows wife or friend or work. While we are, this is. If we lose this, we lose all.
— C.S. Lewis, The Problem of Pain