To Kill a Mockingbird

If you're referring to the lies Dill told about his father the answer is simple. He was describing the father he yearned for, not the father he had. One of Dill's favorite things about the Finch family was the love and acceptance he felt while he was with them. Dill didn't have this in his own life, so he became a part of theirs. The small part of Dill that refused to acknowledge his feelings led him to tell lies that made him feel better.