He could also cope by trying to find small acts of rebellion. Like when Vernon is yelling at him, Harry might give a small smirk or not show the fear that Vernon wants to see. And he may be secretly practicing magic in his room, which gives him a sense of power and control in a situation where he is otherwise powerless. This helps him to mentally distance himself from the torture.
Harry might cope by retreating into his own thoughts and memories of his parents and the wizarding world. For example, he could think about the good times at Hogwarts to endure Vernon's torture.
Harry could cope by making connections with the few kind people around him. Maybe Petunia has a moment of weakness and shows some kindness, and Harry holds on to that. He might also use his intelligence to outwit Vernon at times. For instance, if Vernon tries to starve him as a form of torture, Harry could find ways to sneak food without getting caught. And he would be constantly hoping for the day when he can go back to Hogwarts and be away from Vernon's abuse.
In some fanfictions, Harry might cope by finding solace in his friends at Hogwarts. He could talk to Hermione and Ron about what Vernon does, and their support gives him strength. For example, they might encourage him to focus on his magic studies as an escape from the Dursley's household.
He survives through his strong willpower. Harry has always been a determined character, and that could help him endure the torture.
He might turn to his studies more intensively. Since he has no friends to distract him, he could pour all his energy into learning new spells and magic, becoming more powerful in the process.
Harry might maintain his sanity through his memories of Hogwarts. The thought of his friends, the magic he has learned, and the happy times at school could be his mental refuge. For example, he could recall the fun times in Potions class or flying on his broomstick during Quidditch matches.
In some fanfiction, Uncle Vernon develops by becoming more accepting. For instance, he may start to see Harry not just as a freak but as a person with unique abilities that can be useful. He might begin to tolerate the wizarding world a bit more, especially if he realizes that Harry can use his magic to protect the family from certain threats.
One possible plotline could be that Harry uses his magic in self - defense and this leads to a whole new set of challenges as he tries to hide it from the wizarding world while dealing with Vernon's continued abuse. Another could be that the Dursleys finally get caught by the wizarding authorities for their mistreatment of Harry, especially Vernon's torture.
After Sirius dies, Harry is in a really tough place. He feels like a part of his family has been ripped away. He may start to question his own actions that led to Sirius being in the Department of Mysteries in the first place. Harry will also feel a sense of loneliness, even with his friends around. But over time, he'll remember the lessons Sirius taught him, about being brave and standing up for what's right. This will give him the strength to move forward, and he'll use his memories of Sirius as a source of motivation in his fight against Voldemort.
He might cope by focusing on his training. Harry could see it as an opportunity to become stronger without distractions. He would pour all his energy into learning new spells and improving his magical abilities.
Harry might rely on his own wits and magic. Since he has some natural magical abilities, he could use them to fend for himself, like conjuring food or finding shelter.
It can change the perception a great deal. By showing Harry as tortured and broken, it adds a layer of darkness to the generally more hopeful and adventurous world of Harry Potter. It makes readers realize that there are more sinister aspects that could have happened within the wizarding world.