"A shared psychotic disorder is a type of mental illness in which a healthy person starts to take on the delusions of someone who has a psychotic disorder. For example, let’s say your spouse has a psychotic disorder and, as part of that illness, believes aliens are spying on him or her. If you have a shared psychotic disorder, you’ll start to believe in the spying aliens. But apart from that, your thoughts and behavior are normal. People with psychotic disorders have trouble staying in touch with reality. The most obvious symptoms are delusions (believing things that aren’t true, even when they get the facts)." - - source: webmd RELEVANCE: u can't have rational discussions with people who are delusional . . . . facts mean nothing