Neville used to feel like he was stumbling through life. He could almost picture himself becoming someone but the steps to get there never seemed clear enough. Sometimes he would glance around and see Hermione walking confidently through the library searching for the next piece of knowledge or see Harry striding through the halls with confidence, probably on the way to his next adventure. And he would think and dream of a day when he could have a purpose like they did which caused them to walk so smoothly.
He wanted it with all his heart.
Then Neville went through seventh year and this time there were no Hermione's or Harry's to walk behind. Instead of them he saw the pain and fear in the eyes of the younger children. The sight of it made his heart ignite and that fire gave him what he had been searching for- a reason to step strongly. So he did just that, he stood up and insulted the Carrows to save some nameless second year. The pain was nothing compared to the gratitude he could feel coming from behind him.
He kept doing it. Every day he would a new way to hold back the desperation of those around him. An insult shot at Alecto. A refusal to do as Snape said. Standing in front of everyone else when Amycus wanted to practice the Cruciatus curse in Dark Arts class.
Neville made himself a shield to protect everyone else. He walked boldly through the halls with his head held high until it had finally become to dangerous to do so. When that happened, he retreated to the Room of Requirement and taught the others how to stand up for what was right. And when Harry returned, ready to face Voldemort for the last time, Neville finally felt he was worthy of walking tall and proud by his side. Neville had stopped his stumbling and started doing.
And it felt wonderful.