In Lord of the Flies, Simon is a complex character. He is different from all the other boys who exist somewhere between the boundaries set by Jack and Ralph. Simon has been less conditioned towards good behavior and his goodness comes from his innate spirituality.
In chapter 7, "Shadows and Tall Trees," the boys are beginning to exist within their new reality of the island without even realizing that it is definitely not a normal environment. Even Ralph "discovered...that these were the conditions he took as normal now and he did not mind." Simon tries to reassure Ralph when her recognizes Ralph's anxiety - "You'll get back all right."
In the search for the beast, the boys realize that it is getting late and Piggy has been left on the beach to look after the "littleuns." To go through the forest "by himself? Now?" is a daunting prospect but Simon immediately volunteers and doesn't even give Ralph a moment to consider it before he has "climbed into the forest" and out of sight.