As long as you keep your party alive you're not a failure of a healer as you are doing what your real is meant to do. As someone else said, dpsing is something advance, and I still think it's not something you're supposed to do. It's just something extra that you can do if you want to further push yourself and just make a dungeon go somewhat faster. Unless you're doing raids and ex fights, then that's entirely different story. I'm just hoping this doesn't turn into another one of those topics.
