erlebnis - (n.) an experience that one feels most deeply, and, in a sense, 'lives through'; not just a mere life experience but something memorable that happens to someone [German]

The fight in the Department of Mysteries.

The fight when Dumbledore died.

Leading Dumbledore's Army during his seventh year. The Battle of Hogwarts.

Obviously Neville couldn't call them "happy" memories. They were full of pain, terror and even death.

And yet, he couldn't quite call them "bad" memories either. Even now, years later, they made his heart beat a little quicker and even brought a sort of painful smile to his face.

He had quit Auror training. To his grandmother's chagrin, he had lost all desire to follow in his parents' footsteps any further. Whatever he was meant to do with his life, he realized that that wasn't it.

And yet…

He had helped do something great. And he believed that all those fights, those battles, those awful memories had made him a better person than he would have been otherwise.

His teenage years had been awful. But somehow, that didn't make them any less important.