One reason could be that he doesn't want his friends to worry. Harry often takes on a lot of responsibility and might see his sickness as a burden he doesn't want to place on others. Another reason could be related to his enemies. He might fear that if Voldemort or his followers find out he's sick, they'll see it as a weakness and target him more aggressively.
He could be hiding it out of pride. Harry has shown great courage and determination throughout his story. Being sick might make him feel less like the hero he's supposed to be. Also, he might be worried about how the teachers at Hogwarts will react. He doesn't want to be coddled or treated differently, so he keeps his sickness a secret.
Well, it might start with Harry subtly avoiding certain situations where his sickness could be revealed. For example, he might skip Quidditch practice, making up excuses like he has too much homework. Then, as the story progresses, his friends might start to notice little things, like he looks paler or he's more tired than usual. But Harry keeps coming up with believable lies to cover it up.
One reason could be that he wants to avoid unwanted attention. In the fanfiction world, being overly intelligent might make him a target. Another reason might be that he is trying to fit in with a certain group that values other traits more. For example, if he's in a group that values physical strength over intelligence, he may hide his smarts to seem more like them.
One reason could be fear. Maybe Harry discovers something about Dumbledore in the fanfiction that makes him scared, like a hidden agenda. Another reason might be to protect Dumbledore. Harry could think that by hiding from him, he is keeping Dumbledore away from some sort of danger that is related to Harry himself. Also, it could be due to a misunderstanding. Harry might misinterpret something Dumbledore does or says, and as a result, decides to hide from him.
Try Hiding Again was a science fiction novel written by Jin Xian. The story was about Ye Yao discovering that he had fallen in love with his friend Lu Xun, and the friendship and emotional entanglement between the two. This novel was famous for its ups and downs in the plot and its excellent writing style, attracting the attention of many readers. The novel had a total of 81 chapters and a total word count of about 370,000 words. It was still being serialised. The latest chapter was Chapter 81, Side Story 3 (13), updated on March 4th, 2022. In addition to sci-fi elements, the novel also touched on topics such as friendship and love.
She could be hiding from those who want to harm her. In the wizarding world, there are always threats, and hiding as an animagus is a clever way to stay safe.
She might be embarrassed. Ticklishness can seem like a silly or vulnerable thing, so she doesn't want others to see her react in a way she might consider uncool.
One possible reason could be that Harry has discovered something about himself or his past that he thinks Dumbledore might not approve of or might try to stop him from exploring further. For example, if he found out some dark magic connection in his family history that he wants to understand on his own without Dumbledore interfering.
Maybe he wants to keep it safe from thieves. There could be dark wizards or even some of his schoolmates who might be tempted to steal it.
In some fanfictions, Harry might hide his money in a secret compartment of his trunk. He could use magic to create a hidden space where no one else can find it.
He might pretend to not understand complex concepts. For example, when others are discussing advanced magic theories, he could act confused even though he actually gets it.