In Chapter 6, The Tin Woodman uses a fallacy to explain why it is important for him to obtain a heart from the Wizard of Oz:
The Tin Woodman knew very well he had no heart, and therefore he took great care never to be cruel or unkind to anything.
‘You people with hearts,’ he said, ‘have something to guide you, and need never do wrong; but I have no heart, and so I must be very careful. When Oz gives me a heart of course I needn’t mind so much.’
The Woodman is extra careful "never to be cruel or unkind to anything" because he is afraid that his heartlessness makes him predisposed to unkindness and cruelty. It is easy enough for the narrator and reader to spot the flaw in his logic. His extreme care is precisely what constitutes his heart. He is under the impression that everyone else has a built-in moral compass that means they do not have to take care not to hurt others. He thinks that once the Wizard gives him a heart of his own, he will be able to relax and stop trying so hard to be considerate. But the reader, who of course has a heart, understands that doing the right thing is not an automatic process. Having a heart often means making difficult decisions based on a great deal of care and consideration.
The Tin Woodman's fallacy not only highlights his lack of self-awareness but also urges the reader to develop a stance on morality. By recognizing that the Woodman is wrong about what it means to have a heart, the reader must come up with their own definition. In fact, Baum encourages the reader to see that the Tin Woodman's conclusion is dangerous. If people believe they are innately good and "need never do wrong," they will never think about the consequences of their actions.