Final answer:
The customer's anger is more likely related to a larger trend rather than specific incidents, as there is a change in demand for postal services due to a shift toward digital communication. The post office is making efforts to manage demand and improve customer service by optimizing waiting times.
Step-by-step explanation:
Why the customer is angry can depend on a variety of factors which might affect their experience or expectations negatively. However, in the context provided, the dissatisfaction may not be related to any of these listed options directly. Instead, the context discusses a shift in consumer preferences, indicating a change in demand for the Postal Service, as people move away from traditional snail mail to digital messages.
This indicates that the customer's anger could be related to a larger trend of decreasing reliance on postal services. Additionally, an experiment at the post office with a single main waiting line that reduced the standard deviation of waiting times from 7.2 minutes to 3.5 minutes for customers suggests that the organization is working to optimize its services by improving efficiency and reducing wait times.