It's not that serious. This should be related to his personality and growing environment. The purpose of what he said is to make people agree with him and his key points and attract others' attention. It should not be said that this is a mental illness. As a family member, we should communicate with him more, care for him more and encourage him more. When you meet what he says is right, you should agree with his point of view, and when you are wrong, you should say it in a more euphemistic tone. Don't accuse him of his mistakes to his face, especially in front of outsiders. I hope my answer can help you.