Yeah, it seems to me fairly obvious that if someone implied before a test that I would fail, and I had cause to trust their opinion, I'm not likely to do as wel

Yeah, it seems to me fairly obvious that if someone implied before a test that I would fail, and I had cause to trust their opinion, I'm not likely to do as well as I would have because of the nagging self doubt etc. No change on my innate ability to do the test, but the level of application and focus would be drastically different. (On the other hand it can go far enough as to improve focus, sometimes. "I'll show them", "I failed last time but I know I can do it", etc)