I have always found the prophecy story-arc through-out the Harry potter books to be especially intriguing. In some respects, I've always thought it was a "hat tip" to the conceptual butterfly effect‡. A simple choice being the deciding factor between being the chosen one, or being (in poor Neville's case) one of life's "unlucky people".
I can't seem to recall if Neville ever becomes aware of his own importance, the significance that he and his family's fates played in the "chosen one" prophecy?
If he didn't know, then can we assume that J. K. Rowling orchestrated his important role and sense of defiance in the last "fight" (battle?) scene as a way of showing the reader (or viewer if you're watching the films) that Neville had the characteristics required to become the "chosen one" had fate played out differently?
‡: Quoting from the relevant article on Wikipedia:
In chaos theory, the butterfly effect is the sensitive dependence on initial conditions in which a small change in one state of a deterministic nonlinear system can result in large differences in a later state. The name, coined by Edward Lorenz for the effect which had been known long before, is derived from the metaphorical example of the details of a tornado (exact time of formation, exact path taken) being influenced by minor perturbations such as the flapping of the wings of a distant butterfly several weeks earlier.