How is it possible?

[Rjain]

That's using a term incorrectly then if you are referring to gear and a class. I'm with the understanding that there was a time people would play one role and master it and as a result, call that their main.

I'm playing a warrior, he is my main. All content he is first priority thus making him a main class.

Or you can play several roles and master all the classes.

While people typically only have one "main" class for raiding, some groups are flexible and they don't always go as the same roles. There are many people with equally high item levels on their jobs and have mastered how to play them.