Thinking again about the Lich King, specifically when Arthas Menethil wore the Helm of Domination, always brings me to speculate on his seeming need to prove something. Everything we experienced in Wrath of the Lich King seemed calculated towards that end. From the encounter with him in Howling Fjord through the complicated Drak'tharon Keep and Zul'Drak storylines to the final showdown atop Icecrown Citadel, Arthas always had a plan, and that plan was in part simply to cause his own enemies to provide him with a cadre of such power that he could turn and use against the world, yes. But more than that, Arthas seemed obsessed with proving that he was right.
Again and again Arthas as the Lich King put mortal heroes through situations that served to illustrate his own fall - again and again, he sought not just to torment and inspire hatred and anger just as he had been tormented by Mal'Ganis and grew to be consumed by hatred, but to show by so doing how his own actions had been correct. That the only possible response to what he'd undergone was to become as he had. Even merged with Ner'zhul in the form of the Lich King, Arthas' mind and personality came to shape the entity, and when all roads converged atop Icecrown, it was Arthas' desire to show Azeroth how right he was that shone through.