To know ahead of time what you're looking for means you're then only photographing your own preconceptions, which is very limiting, and often false.
My writing isn't actually guided by issues. I know it seems that way, but I don't sit down and think, Oh, there's this issue I'm bothered about. I only write about things that directly impact my life. When I write, there's a pain that I have to reach, and a release I have to work toward for myself. So it's really a question of the particular emotional circumstance that I want to express, a character that appears, a moment in time, and then I write the play backwards.