Liar, Liar tells of young people who feel they are immortal and not accountable for their actions. Sean is unable to escape his past and is forced to deal with old behavior patterns and habits in a new situation. All people are ultimately responsible for their actions and deeds, as Sean learns. The reader is pulled into the ways Sean thinks and handles his problems, which includes lying. He longs to be close to his father, resents his parents' divorce, and dislikes the man his mother dates.

Doubted by some, he eventually proves himself trustworthy. These are issues familiar to many young people. Readers are confronted with Sean's feelings of guilt after Marsh's death. They can learn from Sean as he makes peace with himself because it is not his fault that Marsh is dead and he is alive.