At the end of the novel, To Kill a Mockingbird (by Harper Lee), Atticus tells Scout, "Most people are, Scout, when you finally see them."
Here, Atticus is making the distinction between looking at someone and really seeing them. If one only looks at another person, they fail to see who they really are. It is only when one sees someone that they can determine the truth about them.
Scout has just learned an important lesson in life. She has learned that people are not always what others state them to be. In regards to Boo, for far too long, the community has allowed rumors about who he "is" to define how all others saw him. It is not until Boo saves Scout and Jem that the perception of him changes.
Therefore, the lesson Atticus teaches Scout is that a person needs to rely on thier own feelings about something--they should not rely on the perceptions of others to dictate how they should see people.