And David Simon says it's a true story: https://newrepublic.com/article/38982/wire-ripped-real-life
I was once told that I was too calm for my poly and then asked why. My response was I didn't trust the science, or the fact that it was a couple week course. That didn't go over well, I ended up taking two more after that and they gave up.
I've seen the other-side of it though where good people failed their poly because they had too low a baseline like I did, caused by medications.
It's really a bunk science. I can get it as a scare tactic, but the fact the the Govt. still relies on it at a higher level is ridiculous.
Maybe that's true in Canada (don't know) but it doesn't matter because psychologists are no better at detecting lies than a typical person of similar education, intelligence and age.
It might be psychological warfare.
I would wager that a surprisingly large number of people think that polygraphs detect lies. An even larger number are probably open to the possibility.
If you hook up somebody in that group to a polygraph, you probably rocket their stress levels through the ceiling, which might push them to crack. Behavior under stress is a fascinating thing.
Honestly, I had a snarky comment ready for a comment lower-down about the rationale for polygraphs, but I thought about it a bit, and can't, off the top of my head, come up with a faster, cheaper, and safer way to put that kind of stress on a person.
Useless against somebody trained -- like, say, an intelligence operative -- but it might not be as stupid as it appears on the surface.