Thenceforth, in the nature of things, he would possess an abiding distrust of appearances. He would have to learn the reality of a thing before he could put his faith into it.

What was reprehensible in being fearful in the presence of the unknown?

Washburn has reported that infant baboons and other young primates appear to be born with only three inborn fears -of falling, snakes, and the dark-corresponding respectively to the dangers posed by
Newtonian gravitation to tree-dwellers, by our ancient enemies the reptiles, and by mammalian nocturnal predators, which must have been particularly terrifying for the visually oriented primates.

We fail so easily to see the difference between fear of the unknown and respect for the unknown, thinking that those who do not hasten in with bright lights and knives are deterred by a holy and superstitious fear. Respect for the unknown is the attitude of those who, instead of raping nature, woo her until she gives herself. But what she gives, even then, is not the cold clarity of the surface but the warm inwardness of the body - a mysteriousness which is not merely a negation, a blank absence of knowledge, but that positive substance which we call wonderfull.

Though not fearful of measurable dangers, she feared the unknown.

Superstition is the child of ignorance and fear.

She feared the unknown as we all do, and her ignorance made the unknown infinitely vast.

Fear breeds superstition.

I had to act with the utmost circumspection to save myself from the suspicion of insanity. My memory of the Law, of the two dead sailors, of the ambuscades of the darkness, of the body in the canebrake, haunted me; and, unnatural as it seems, with my return to mankind came, instead of that confidence and sympathy I had expected, a strange enhancement of the uncertainty and dread I had experienced during my stay upon the island. No one would believe me; I was almost as queer to men as I had been to the Beast People. I may have caught something of the natural wildness of my companions. They say that terror is a disease, and anyhow I can witness that for several years now a restless fear has dwelt in my mind, such a restless fear as a half-tamed lion cub may feel.

His mind was destitute of that dread which has been erroneously decried as if it were nothing higher than a man's animal care for his own skin: that awe of the Divine Nemesis which was felt by religious pagans, and, though it took a more positive form under Christianity, is still felt by the mass of mankind simply as a vague fear at anything which is called wrong-doing. Such terror of the unseen is so far above mere sensual cowardice that it will annihilate that cowardice: it is the initial recognition of a moral law restraining desire, and checks the hard bold scrutiny of imperfect thought into obligations which can never be proved to have any sanctity in the absence of feeling.

He had no conscious knowledge of death, but like every animal of the Wild, he possessed the instinct of death. To him it stood as the greatest of hurts. It was the very essence of the unknown; it was the sum of the terrors of the unknown, the one culminating and unthinkable catastrophe that could happen to him, about which he knew nothing and about which he feared everything.

"We have simply been too fearful to go into that place."
"You? Fearful?" I doubted this.
"Do not mistake my arrogance for courage, my son. It is true that I am renowned for what I can do. But I am afraid of the unknown, as are most men, Gamesmen or pawns alike."

There's always fear of the unknown where there's mystery. It's possible to achieve a state where you realize the truth of life and fear disappears, and a lot of people have reached that state, but next to none of them are on Earth. There's probably a few.

Slowly but inexorably crawling upon my consciousness and rising above every other impression, came a dizzying fear of the unknown; a fear all the greater because I could not analyse it, and seeming to concern a stealthily approaching menace; not death, but some nameless, unheard-of thing inexpressibly more ghastly and abhorrent.