Gary Paulsen devotes a large chunk of Liar, Liar to Kevin’s excuses for lying. Kevin’s character arc happens in three phases over the course of the narrative. Initially, Kevin feels comfortable using dishonesty to get what he wants. He avoids guilt and shame by convincing himself he isn’t hurting anyone, and framing his lies as helpful to others. In the second phase, Kevin develops insight into the negative consequences of lying and the value of honesty. The third phase shows Kevin acting on his realizations and making amends. Kevin’s true motives in the first phase reflect the same reasons many people lie, and his justifications reflect another human tendency: rationalizing dishonesty to maintain a positive self-image.

Paulsen makes a clear distinction between Kevin’s desires, which are in and of themselves based on an acceptable level of self-interest, and the methods he uses to pursue those desires, which cross moral lines. Kevin wants to get rides from his older siblings, to impress a girl he likes, and to get a break from JonPaul’s frustrating obsessions. The way Kevin goes about getting what he wants—telling lies that range from disrespectful to dangerous—define his motives as selfish within the moral framework of Paulsen’s novel.