For every greatness there's a cost. It can be something you earned, learned, owned, hoped or unexpected. Since the day that magic existed in this world a lot of people have sacrificed themselves to make it last and most importantly to make it last for a greater cause. This is why Hogwarts was built in the first place. They needed to teach people to control their abilities, educate them on their capabilities and how they can use it for the betterment of this world.

Unfortunately, there's always someone who goes out of the line. Sometimes, they don't want to, but accidentally they take that darker path. And at other times they experiment on what would happen if they chose that path. Others simply want to dominate the world in their own terms. This is what happened to Lord Voldemort. He actually had a combination of all these three incidents. His family background and his childhood had a lot to do with his dark magic. His mother had little magic in her. As a result when he fell in love with Tom Riddle, a muggle village boy, she seduced him with a love potion. After sometime, Merope thought that it would be time to get Tom Riddle Sr. out of the love potion. However, he left after that. Soon after Tom Marvolo Riddle was born. As his mother died at his birth, he was left in an orphanage where he was bullied. 

Because of his unfortunate turnout, a lot of people had to sacrifice themselves for his cost. There were his own followers who he killed because he felt that urge of leadership. There were other witches and wizards who sacrificed themselves to avoid him from destroying the magical and the non-magical world. Moreover, there were a lot of non-magical people who died without having any idea on what's going on. 

Although he took away the lives of countless great men and women, this book will have a look into the lives of James and Lily potter, Professor Albus Dumbledore, Severus Snape, Sirius Black, Professor Moody, The Weasley family, Dobby, Remus Lupin, Nymphadora Lupin and Cedric Diggory. All these people sacrificed themselves and their families to end this never-ending war. At last, they got that peace that they were looking for. And, Harry Potter made sure their sacrifices did not go on waste. But, however a life is a life, and it cannot be replaced. 

If Voldemort was never born, if Dark Magic never existed, if Voldemort's grandfather had been more kind and less proud of his descends, if he acted more of a fatherly figure and helped his daughter, if the professors were more aware of Tom Riddle none of this disasters would happen. But, change is inevitable. Therefore, we have to conform to it. A lot of people regretted on the actions that happened. Especially professor Slughorn, who first gave him the idea of horcruxes. Albus Dumbledore always wanted to transform Tom Riddle's abilities for the "greater good" as he was apparent of his immense talents. However, all these took a dramatic change when Riddle found out that he was the heir of Salazar Slytherin, and that he felt the need to finish what Salazar Slytherin started; Getting rid of the muggles. 

However, as mentioned before there were a lot of people who were determined to protect them. And as such they created the "Order of Phoenix", a secret organization of witches and wizards who have committed to fight against Voldemort. They fought till the end, and most of them sacrificed themselves in this battle. Taking them as the inspiration, the young witches and wizards of the new era who are at Hogwarts formed the "Army of Dumbledore" and they were to help Harry in defeating the Dark Lord. Although, they were young they had such bravery that they chose to fight the final last battle, which was the most deadly of all. 

This book is an inspiration for being brave irrespective of your status or decent. It also tells that what's done is done. Maybe you committed crimes in the past. But, when you have the ability to fight against those consequences, you have to do it. Because that's what makes you worthy. All these people had different pasts. Some of them were good from the beginning; others had no idea on what they were getting into, while others were a part of Voldemort getting this stronger. But, in the end they chose to fight for what's right because there's a way to make your hope a reality.