From the Mayo Clinic - "Narcissistic personality disorder (NPD) is a mental disorder in which people have an inflated sense of their own importance, a deep need for admiration and a lack of empathy for others. But behind this mask of ultraconfidence lies a fragile self-esteem that's vulnerable to the slightest criticism.

A narcissistic personality disorder causes problems in many areas of life, such as relationships, work, school or financial affairs. You may be generally unhappy and disappointed when you're not given the special favors or admiration you believe you deserve. Others may not enjoy being around you, and you may find your relationships unfulfilling."

"Narcissistic personality disorder treatment is centered around talk therapy (psychotherapy)." 

And trumps hand picked advisors reinforce his grandiosity - "It was a huge crowd, a magnificent crowd. I haven't seen such a crowd as big as this," Hoyer told CNN, quoting Trump.

Who tells him he's not always right? No one.