Mack thought hard about what the man said, thought about what he knew about essence, warlocks, his own training, and finally said, "I have no clue".
The professor slapped his own face in frustration, but eventually said, "Sigh, I was expecting too much. It's normal for you to not know, after all, this is a very complex subject, and one that is normally regarded as 'mysticism' rather than science, all that involves the cultivators is treated as such, and because of that, people rarely teach this or try to research this topic."
Mack keep pondering what the professor said, and for him, those cultivators were indeed akin to mythological creatures. He rarely heard about them, even the old man knew very little. That, for itself, showed that it was a very grey topic. With not much information circling around.