A knight has a stubborn head, covered in an iron helmet. For the Mentor it is hard to get through that, but in many stories an older, wiser parent figure is at hand to guide the initial clumsy steps of the child
The Mentor isn’t always included and he can turn up anywhere in the story, but it’s usually right before the departure to the Special World. As discussed in Part 3, he might help the hero to overcome his last reluctant fear before leaving the Ordinary World.
In Star Wars, it’s Obi-Wan that guides Luke, even gives him his father’s light-saber. In E.T., one hero is at the same time mentor for the other hero: E.T. steps in for Elliot’s absent father and guides him through high school experiences like the first kiss and teaches him about coping with loss.
Honestly, I love the Mentor in stories. It makes you feel safer and the scary truth becomes less frightening. Unfortunately, it is necessary for the Mentor to leave at some point, or the hero will never develop on its own.