Answer:
Explanation:
As the chapter is from Harry's point of view, we can see her stream of thoughts and feelings. It is described how the nostalgia for Hogwarts is giving him a stomachache, how he feels so lonely without any friends and family to celebrate with him, and how he is spending his birthday feeling miserable.
If the chapter was from a different point of view, for example, Dudley's, we couldn't have seen why Harry's birthday is so sad and therefore called 'the worst', and we could not realize how all events are affecting his state of mind and emotions. The main point would be completely different, as the events would be described differently, in a different manner and with the completely other goals of the narrative.
