There was a man who once proposed a hypothetical experiment. In the experiment, a cat is placed in a box. Inside the box is a device that causes a poison gas to be released if a radioactive isotope hits a certain sensor. There is a fifty-fifty chance that this will happen. The question then is how to determine whether the cat is dead or alive without opening the box. The man who proposed the experiment believed that until the box was opened, the cat would be in a state of flux, both dead and alive, it would be at the point in which the box is opened and the results of the experiment observed that reality would collapse to an either/or state.

What if the cat escaped the box before it was observed and reality collapsed one way or another though?

He stood on the battlefield, they both stood on the battlefield, fighting different opponents. Somehow, they both still were despite the fact that they both were together.

Perhaps something was keeping the observation from being made?

It had to be the mask. For as long as everyone around him but the Other didn't know who he was, for as long as they were uncertain, they would exist. As soon as someone realizes though, he has a feeling that one of them would disappear since they both couldn't be together. The mask would have to stay on at all costs. He had a feeling that if one of them were to vanish, it would be him.

You can't be both alive and dead at the same time, in the same universe after all.