I don't think the ability to sprint/go hard at the end has to do with not working hard enough the rest of the race but about having enough fuel/nutrition in you to power that last burst of energy. IMHO.

I also think its one of those things that comes from training and race experience. The more you race and try different strategies, the more you are going to learn about your bodies capabilities. Pacing and pushing yourself will become instinctive.

More specifically: For that last kick to the finish line, I can't imagine going for more than 400 meters. A 400 meter sprint is pretty darn long. But I would start picking up the pace then and then really kick it in high gear the last 200 to 150 meters