A man believes several world governments are secretly in contact with him about an invention, but cannot produce any evidence of this contact when asked directly. Why does his inability to produce evidence not resolve the belief?
A grandiose delusion, like any delusion, is not held provisionally pending evidence — it is a fixed conviction maintained regardless of whether supporting evidence can be produced. This is precisely why simply pointing out the absence of evidence, on its own, does not and should not be expected to resolve the belief; the fixity is the defining feature, not a gap in the person's reasoning that more searching would fix.
References
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 4, 'Disorders of Thought and Speech'.