Uh… because belief feels like truth from the inside, and so you cannot trust the inside view unless you are extremely well calibrated on tiny probabilities? So all you are left with is the outside view. If that is what you are asking.
I think you should distrust the other person for other reasons. They may have ulterior motives, for example—as you wrote, they may be lying. There are many social reasons for them to make claims like that. Whatever lies we tell ourselves, they are usually not conscious and explicit.
Which is why I found it strange that you stated this claim without further explanation.
Uh… because belief feels like truth from the inside, and so you cannot trust the inside view unless you are extremely well calibrated on tiny probabilities? So all you are left with is the outside view. If that is what you are asking.
I think you should distrust the other person for other reasons. They may have ulterior motives, for example—as you wrote, they may be lying. There are many social reasons for them to make claims like that. Whatever lies we tell ourselves, they are usually not conscious and explicit.
Which is why I found it strange that you stated this claim without further explanation.