Remember that in your mind there is only one person home: yourself. Within your mind, only you have dominion. Interesting enough, outside of our minds, within reality we share a space with others in which individuality is a rare resource. The real world is filled with multiple perspectives that often collide in ever evolving ways. Despite this, some individuals manage to claim high dominion over their mind realm: the mind itself and all that occurs within it.
I would venture to say that achieving dominion over the mind realm requires traversing all the sub-realms within the mind realm. One would need to explore the darkest and most powerful of sub-realms and conquer them. In conquering the dark realms, one attains power over the darkness and negativity that exists in these spaces. Attaining control over the darkness allows one to have the ability to tame and defend against any and all darkness. This is a valuable power.
Outside of the dark realms there are the positive realms, the realms where one learns of the immense and beautiful capacity for all things good that one is capable of giving and receiving. The positive realms are good realms, they are the realms in which one reclaims any lost powers and improves upon them, as well as gaining new powers that prove to be triumphant in all obstacles that wish to deter oneself from achieving peace and great mastery over oneself. The good realms are meant to be achieved, mastered, and befriended. It is within the good realms that oneself achieves ultimate mastery in channeling all things good and positive, which is a power too powerful to be neglected or refused of mastery.
Having mastery over the dark and negative realms, as well as the good and positive realms, provides oneself with the power to conquer and claim dominion over all that would act as an obstacle.