I don't know for certain, but gut feel is that most folks in the military get approved for clearances, unless, as stated, you really have some truly major issues. And if you did have a major issue, you really shouldn't have the clearance. Most military who apply are doing so because they actually need it to be a contributing member in their command. I even know of some folks that had "snags", but still ended up getting cleared. These investigators recognize that. But if they can't clear you, you basically have to go into a different job/designator.