Why does Simon go off alone in Chapter 7 of "Lord of the Flies"?
Simon, right at the start of the chapter, makes his prediction to Ralph that Ralph'll get back all right. He's already behaving in an "other" sort of way - slightly unusual, slightly mystical. And so his disappearance doesn't come as much of a surprise.
Though Golding does give us a practical reason for it. Ralph remembers that they've left Piggy alone with the littluns, and feels guilty:
'We can't leave the littluns alone with Piggy. Not all night.' The other boys said nothing but stood round, watching him. .
'If we went back we should take hours.'
Jack mocks Ralph, but Ralph insists that someone has to go:
'Someone's got to cross the island and tell Piggy we'll be back after dark.'
Bill spoke, unbelieving.
'Through the forest by himself? Now?'
'We can't spare more than one.'
Simon pushed his way to Ralph's elbow.
'I'll go if you like. I don't mind, honestly.'
Before Ralph had time to reply, he smiled quickly, turned and climbed into the forest.
There you have it. He goes back to Piggy to help him look after the littluns.