What does the speaker attribute blame for the situation to?

The speaker attributes the blame for the situation to Charlotte for letting them down, indicating a specific focus on Charlotte's perceived failure or absence in fulfilling expectations. This suggests that the speaker believes Charlotte had a responsibility or role that she did not adequately fulfill, leading to the current predicament.

In this context, the emphasis on Charlotte signals that the speaker feels personally affected by her actions or lack thereof. This choice implies that the speaker feels a sense of disappointment or betrayal, which is a strong emotional response often associated with interpersonal relationships where one party relies on another.

The other options present different potential sources of blame but do not align with the speaker's expressed sentiment. For instance, blaming one's own actions would indicate self-reflection and responsibility, while attributing blame to the postman's negligence or a lack of communication suggests other external factors at play rather than placing personal accountability on Charlotte.