Mental illness is different for those who are relativists and those who are absolutists. Relativists believe untrue things are true sometimes. This is called "delusion" by psychiatrists. Absolutists avoid false beliefs because they demand proof for their beliefs. They are more immune to mental illness. Those who think rationally have a more well defined reality than those who think in relative terms.

You are so right about mental illness. I started hearing voices when I was meditating on why demons exist. I wanted to know if Hell was real. I now know after twenty four years of hearing demonic insanity that some people suffer from cognitive deficiency, which leads to frustration because of the lack of ability to succeed. In other words, some people live in Hell. I am lucky enough to be able to keep above believing false beliefs, but many people try to deceive you causing mental illness.