Harry’s childhood affects him enormously, setting the stage for huge swathes of his behaviour throughout the books. It doesn’t start and end with exceptional reflexes and the ability to go for long periods of time on not much food.

For example: Sirius Black is the first adult in whom Harry Potter willingly confides before he’s beaten the bad guys and taken care of the issue on his own.

This happens in book four of seven.

Look, Harry has trust issues: he lets very specific people in and they stay there. End of. Everyone else spends a lot of time bashing their heads against the brick wall that he throws up around those people he loves.  

But noticeably, all of the people he loves in that way are teenagers like himself; all but Sirius. Never in five books does Harry ever confide in an adult other than Sirius. He accepts guidance from adults when it’s offered to him, but he does not take his troubles to grownups of his own volition. Ever. This character trait drives the entire plot of the first two books – Harry, Ron and Hermione solving mysteries on their own even though they are in a castle stuffed with teachers, among whose number is the man the Wizarding World acknowledges as the greatest wizard alive. They tell all, of course they do. But only when it’s over. Only when they’ve already won.

Harry Potter does not trust people who are in a position of power over him. This isn’t a result of Snape, or Umbridge, or Skeeter-induced Ministry ridicule. This is a result of the Dursleys.