In what ways is the saying you can't judge a book by its cover a good one for the story holes

There is so much more to these boys than just being "criminals". Stanely, for example, is so much more than a "thief". Stanley is an empathetic character: he is a loyal friend to Zero, and a caring son to his parents. He doesn't want to worry his parents, so in Chapter 9 he writes a letter home to his mother that is full of lies about all the fun he is having at Camp Green Lake.