How much of what Sister reports can we believe?
In Eudora Welty's famous short story, "Why I Live at the P.O.," Sister is the classic unreliable narrator, so believe what she says with caution! This story is told in first person, with Sister narrating the events of why she moved out of her family's home and into the post office. As the narrator, she only tells one side of the story—her side. She makes harsh comments about her sister, Stella-Rondo, like that she's "spoiled" and tells "deliberated, calculated falsehoods."
At the same time, Sister portrays herself as the victim and the righteous one in the family, who is undeserving of everyone's criticism. When she makes a sarcastic comment or noise like "H'm!" and when she is questioned about it, she then backtracks by saying she didn't mean a thing. In addition, Sister always tries to cause trouble, like suggesting that Shirley-T is not adopted, no matter what Stella-Rondo may claim.
Sister's behavior, which borders on that of a spoiled child, leaves the reader uncertain of how much she says is true or accurate. It would appear that much of it is exaggeration, simply to gain the sympathy of those around her. At the end, when she leaves to go to the P.O., she takes several small items in a petty way as she has a tantrum over the way she has been treated. This reveals her to be a person who is clearly not reliable or believable.