Ever see a play and realize that you know how it's going to end halfway through (or worse)?  That's not good, because as an audience member, if you already know what's going to happen, you have a lot less incentive to watch the play.  Often, this problem occurs because the characters aren't evenly matched. If one character has more "weapons" than another, then it's likely he's going to run right over him.  Of course, weapons don't have to be actual weapons, nor do they even have to be physical.  For example, Mary might have a secret that June, her boss, doesn't want to come out.  June has power because she's the boss, but Mary has power because she has the secret. With neither character clearly on top, the outcome of the play will stay in doubt until the end, and your audience will stay engaged.