Without going into too much detail, they look for patterns of behavior. It depends on your interviewer. It depends on who your investigator is. It depends on the job. It depends on so many factors it's impossible to say how it will turn out. I know guys who have failed polygraphs, only to be asked to retake them... Then they fail again. So then they retake. And fail. Then retake... Then pass. So you see, part of it is what you can offer them. If you're in demand, they will find a way to pass you. It's incredibly subjective.