Why is "Grown folks don't have hidin' places." relevant with repsect to the theme or symbolism in this book?

When Jem suggests that knothole in the Radleys' oak is an adult's hiding place, Scout corrects him, saying, "'Grown folks don't have hidin' places.'" Jem and Scout discover later in the book that many adults hide behind their prejudices, religious beliefs, and their personal notions of right and wrong.