And he knows that Voldemort made a mistake. And in the last book, I don't know whether it is this that really saved Harry from the death curse or whether it was the fact that he was able to bring all the three objects together at the time of the wand, the cloak and the ring at the time of the curse, and they were all his. Because he had the ring in his hand, the cloak was his, and the wand was technically his, even though Voldemort wielded it