"Still, I should have known better. But I'm not going to argue the point with you. You were asking me about my anger with Remus. Harry, you have no idea how close the Marauders were. We were always there for each other. When Remus lost his mother, when James' parents were killed in an attack, when I ran away from home,…we've seen each other through all those tough times. So naturally, all that time in Azkaban, I assumed Remus would have been taking care of you like a surrogate uncle, and when I found out that you didn't even know of his existence until two years ago…"
Sirius' tone grew cold. "He turned his back on the Marauders just like Peter did. If things hadn't gone the way they had, you'd have been calling him 'Uncle Moony' and he would have been like a second godfather to you. Instead of being there for you, he's distanced himself to such an extent that you call him 'Professor Lupin', like he's a bloody stranger. I know it's unfair to hold it against him, considering I was the one who abandoned you first. And there was no way the Ministry would have allowed a werewolf to adopt the Boy-who-lived. But I can't help but think that he should have made an attempt to at least visit you once."
Sirius sighed and turned to look at Harry. "I don't expect you to understand, Harry. And I don't want to color your opinion of him, though it's a bit too late for that now. I just want you to question everyone's actions around you. At the end of the day, whether someone is a devout Dumbledore follower or a fanatic Death Eater, everyone lives to serve themselves and their family. If you can understand their motives you'll understand their actions."
Harry frowned. Those words were disturbingly familiar to Voldemort's 'only power is real' speech in his first year. "Not everyone is like that, Sirius. My parents died to protect me. You've sacrificed so much to be by my side. There are some people who strive for a greater cause."
Sirius gave Harry a wry smile. "Sometimes, even ordinary people can rise to greatness through a single act of outstanding bravery. But except for that one moment, they're still ordinary people with flaws and all. Your parents were human. I'm human. No one can be a hero all the time. So if anyone gives you an impassioned speech about your role in this war, sprouting words like 'sacrifice' and 'greater good', I want you to turn tail and run as fast as you can in the opposite direction."