How does the difference between the character's spoken words and internal thoughts affect the story

it creates dramatic tension

Explanation:

Often the authors use the thoughts and words spoken by the characters to create a dramatic tension in the story. For example, a character may be experiencing a terminal illness and he is very worried, sad and hopeless, but when someone asks how he is he smiles and says that he is great. This creates a dramatic tension in the story because the reader knows what is happening and what the character says is different than what he is thinking.

the mending wall was written by robert frost