Ok, but probability doesn't work like that. Even if 99.99% of the time a given individual is delusional, you still have to check every time because this person might be the 0.01%. It's like the question of "you flip a coin 9 times in a row, and it has come up heads all 9 times. If you flip the coin a 10th time, how likely is it to be heads?"
Also, and perhaps even more importantly, if you aren't actually checking every time, then you don't actually know what the statistics for delusional vs not are, you're just guessing.
Also, and perhaps even more importantly, if you aren't actually checking every time, then you don't actually know what the statistics for delusional vs not are, you're just guessing.