The ideas of fear and paranoia are prevalent in Lord of the Flies, especially in the example of the beast.
Of course, there is an initial fear of never being found which emerges after the boys realize the nature of their situation. Those boys who realize that there is a chance no one knows they are on the island understand that the possibility of rescue is in no way guaranteed.
The fear of dying on the island infiltrates the boys' thinking and behavior in their time on the island, immediately causing the death of the boy with the birthmark on his face and later leading Ralph to grow desparate regarding the signal fire.
When one of the little boys voices his fears about a beast coming out at night, a measure of paranoia sets in among the group. Fear of the beast is specifically connected to paranoia and projected internal fears by Simon.
Though some of the boys refuse to believe in the reality of any beast on the island, their general fears death and the unknown eventually push them into a belief.
The boys who see the dead pilot on the mountain are all too afraid to see the dead man for what he is. Paranoia takes precedence over reality and the beast becomes established as a fact, leading the boys to move the signal fire to the beach.