Stress
Going in, you know that this is a controversial field. There are some who think polygraphs can be tricked. Others believe the results of a polygraph are not statistically sound.
You'll have to be careful not to let your emotions contaminate the test results or sway the person you're examining in any way.
The evidence gathered in murder investigations or other big crimes could be in your hands. If you misread the results or give a bad test, you could help to put away innocent people or help set the guilty free.
Lucky for you, as stressful as this job can be, you're not under nearly as much stress as the person who is strapped into the polygraph machine in the chair in front of you.