Simon, the "moral compass" in the stranded group is strange because he repeatedly acts just slightly outside of the displayed norm the rest of the group gives. There are many examples of when Simon breaks apart from the group (literally and figuratively–see chapter 8), and says things that seem "off":
"Simon grinned and shook his head.
'How do you know then?'
When Simon was still silent Ralph said curtly, 'you're batty.'
Simon shook his head violently till the coarse black hair flew backwards and forwards across his face. 'No I'm not. I just think you'll get back all right.'"
Simon is also considered strange in how he is innately gentle-natured; while most of the boys are giving in to their primal desires, Simon is kind to Piggy and helps the littluns ("found for them the fruit they could not reach, pulled off the choicest from up in the foliage, passed them back down to the endless, outstretched hands" Chapter 3). These kind-hearted tendencies reveal themselves later to allow Simon to be the only one perceptive enough to discover the "real beast" on the island.