The first misconception is a good advisor, because advisor implicates good and that should say it all. In war every level of actor needs good information about himself, the surrounding, the enemy and even the weather. Bad information can kill and therefore every source of information needs to be put relative to the ability to get out of trouble.
The same applies for Kings. It is important what is said first of all, then who said it and when and why to make an educated decision that will impact lifes of millions or even billions.
Princes are in education to learn valuing both information and source to become rightous Kings and no Tyrann like Louis le 15 or victim to bad sources like the Romanovs did on Rasputin.
There is no rule except that the worst advisors are fear, anger and hate and the best a pure heart.
