A delusion is a falsehood that one believes in.

Wikipedia- "A delusion is a belief held with strong conviction despite superior evidence to the contrary. As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, or other effects of perception."

Anything can spark a delusion to form as long as the individual has strong beliefs in it. I feel one doesn't need to be psychotic to think like so. I think the more intelligent one is, the more delusional that they can become over what they think is right, I.e.- scientists, theorists, religious fanatics, etc.

As far as self-esteem goes, if one thinks along the lines as they being the worlds worse and believes it, then they are delusional about them self and suffer from extremely bad self-esteem probably stemming from severe abuse as a child, C-PTSD, depression, or just plain bad luck.

This is what I would say if I was part of the convo.