He realized that all men were like this; that each person was to himself one alone. One oneness, a unit in a society, but always afraid. Like here, standing. If he should scream, if he should holler for help, would it matter?
Tom is out with Mother looking for Douglas at the ravine. The summer has just begun and Mother fears for Douglas because the Lonely One is around and it is very late at night. Tom realizes as he senses the fear in his mother that to some degree we can never be anything other than alone. We are always a part of a larger group, but we also have only ourselves to rely upon sometimes. It is possible that relying on ourselves might not be enough. Tom understands, although he is only ten years old, that there is evil out there that we might have to confront, and when we do so, there will be no one there to help. Although a community can bring aid, there are times when civilization is too far away.