The wizarding world is much given to prophecy and divination: Sybill Trelawney (mostly) predicts death and the centaurs look to the stars. But Professor Trelawney's predictions don't always come true in the way you expect, and centaurs sometimes simply say: ‘Mars is bright tonight.'
The Harry Potter series is full of examples showing us that, while we might think our future is set by what happens in our past, we don’t have to be what we started out as.
In the case of Harry, we're shown that the path you take is often affected by things out of your control, but you also have a say in it through the choices you make – like his choice to be sorted into Gryffindor, or to be friends with Ron instead of Malfoy.
Of course, these choices are easier to make for some than for others: the children of the Weasley family all did incredibly brave things and made huge sacrifices, which should not be forgotten, but they did so having had the benefit of a loving support network for their entire lives.
This was not the case for Harry, who grew up without his parents and with an absence of any real kindness or affection from his extended family, the Dursleys. For the first 11 years of his life he had no friends, and no one to explain what was actually happening when he did things like make an entire pane of glass disappear.
Even when he had joined the wizarding world he was occasionally sneered at by the likes of Snape for not knowing certain things about the magic that had been hidden from him for so long. Due to his unwanted celebrity status, a lot of Hogwarts students often judged Harry more fiercely when he was put in the spotlight, such as being chosen for the Triwizard Tournament or losing heaps of Gryffindor points.
Malfoy, especially, liked to use Harry's fame against him, especially when he slipped up or was caught in an embarrassing situation. But despite everyone focusing their attention on his past, and the prophecy for his future, Harry eventually grew beyond being The Boy Who Lived, surrounded himself by good friends, conquered Voldemort, and actually managed to get the job he always wanted as an Auror, becoming a legacy in his own right.
Lord Voldemort was an example of someone who tried to overcome their past in the wrong way.
The Dark wizard detested the thought of his sad upbringing and a Muggle father, and became hugely ambitious and determined. He started out not too dissimilar to Harry, also growing up an orphan. However, when we see a flashback of the Dark wizard as a child, we discover that he always seemed a little twisted. Despite early encouragement from Albus Dumbledore to change for the better, Tom Riddle chose the dark path to become Lord Voldemort very easily.
‘His powers, as you heard, were surprisingly well-developed for such a young wizard and – most interestingly and ominously of all – he had already discovered that he had some measure of control over them, and begun to use them consciously. And as you saw, they were not the random experiments typical of young wizards: he was already using magic against other people, to frighten, to punish, to control.’
Harry Potter and the Half-Blood Prince
But while going down a dark path is also a choice, there is always room to choose to be better, despite how you grew up.
Sirius and Regulus Black were from the same pure-blood wizarding family, but Sirius had no truck with his parents’ mania for wizarding purity, and eventually got himself burnt out of his own family tree.
Meanwhile, Regulus followed a more ‘traditional’ path, becoming a Death Eater, but soon came to his senses and realised that Voldemort had to be stopped. Both Black brothers made sacrifices that would have gone against their family's wishes, and proved that what is right isn't always what is easy – in two very different ways.
Grindelwald began his life in a callous way, and was expelled from his school for some of his many wrongdoings. But even Gellert Grindelwald, the most famous Dark wizard to rise before Voldemort's time, was said to have shown remorse and, perhaps, tried to make amends for his crimes in later life by lying to Voldemort about the whereabouts of the Elder Wand.
Grindelwald's closest friend for some months in his youth was, of course, Albus Dumbledore. At one time Dumbledore's choice rested on a knife edge. He tells Harry in Harry Potter and the Deathly Hallows that after the death of his mother he resented his family.
‘Do not misunderstand me,’ he said, and pain crossed the face so that he looked ancient again. ‘I loved them. I loved my parents, I loved my brother and my sister, but I was selfish, Harry, more selfish than you, who are a remarkably selfless person, could possibly imagine.’
Harry Potter and the Deathly Hallows
It was the death of his sister that pulled Dumbledore away from a dark future with Grindelwald, though he lived with the pain of it all his life, and tried to make amends in his service at Hogwarts school.
Not all choices are as difficult as those we've seen in the wizarding world, but as Harry and the other characters learned, even the smallest are easier to make if you’re not alone.