What are the effects of megalomania?

Addressing Malik Ashtar, Imam Ali (A.S) wrote: Do not tell people I have been ordered, and I also order (you), so it must be obeyed. This type of megalomania, corrupts the heart, and withers away the religion, as well as destroys the (Divine) blessings. And if with all the position and power which you have, you are inflicted with vanity or megalomania, look (reflect) at the grandeur of the rule of Allah (SWT) as the supreme power, which will save you from that rebellion, and will alleviate your extravagance, and will return your thought and wisdom to its original position [1].

[1] Nahjul Balaghah, Letter 53.