Professor Longbottom is the head of Gryffindor house and the Ravenclaws don’t understand why, because if Professor Potter killed Voldemort, shouldn’t he be head of house? So as Ravenclaws do, they pushed the subject even though it wasn’t their business (mostly because Gryffindors just shrug it off and move on). Ravenclaws asked headmistress McGonagall why, and she just responds with “Because Professor Longbottom is a more exemplary Gryffindor.” And the Ravenclaws are like “what? No?” So they take the matter to Professor Potter and ask him. He just laughs and says, “I fought because I had to, because I was chosen by Voldemort, and was magically linked to him, I had no way out. And Neville was chosen by the death eaters. He faced more enemies personally, and he could’ve ran and hid, but he was the face of the revolution here. Neville stood his ground while I was in hiding.”
And all the Ravenclaws become awestruck and ask for more information, and both professors just brush off the subject. And because the Ravenclaws are who they are, when history of magic has it’s lesson on the war at hogwarts, they pay more attention than anyone and soon have a deeper understanding and respect for Professor Longbottom.
It’s actually common for things to go wrong without it being anyone’s fault.
Your car can break down without it being the fault of the person who borrowed it last week. You may wake up to find the coffee pot is broken for no reason other than it’s quit working, it’s not automatically your roommate’s fault because they touched it last.
Just let things go blamelessly wrong sometimes. It will improve your life.