I suppose if you combine this approach with the theory that nothing is 100% certain you end up with a test that is impossible to get 100% on (which I guess make

I suppose if you combine this approach with the theory that nothing is 100% certain you end up with a test that is impossible to get 100% on (which I guess makes perfect sense as nothing is 100% certain). But back to reality, if you set students tests where a 100% confident answer being wrong instantly meant they fail, it feels like you are no longer testing the student on the subject matter in question and instead are testing their ability to play the probability meta-test game. The task itself of working out how 'confident' you feel about an answer also feels like an impossible task (almost like a non-technical project manager asking a developer how long a task will take). I guess it would be fun to see the results of tests taken using this approach and then compare the scores with the new system, the old system and ultimately what they get as their final grade in the subject.