It is a necessary fuel that spurs a will to survive, to fight back, to not give in to a greater force that can threaten to strip a person of all reason, morals, and humanity. At some points, Jack knows what he is doing is wrong, but he is already so far gone that he prefers being a beast, because he becomes convinced it is better to evoke fear in others than be consumed by it. Ralph by contrast tries to channel his fear and the horrors he witnesses, ie. the murders of Simon and Piggy, Golding is attempting, in this quote, to inform others that mostly all fear is derived from fear