The phrase Mental Control refers to ability to control thoughts in the brain of the physical unit. An individual who is able to exert mental control is to determine, at will, what thoughts and ideas will take up space within the confines of the physical brain. Mental control is a critical aspect of spiritual Awakening. Lack of mental control interferes with awakening and empowerment by stripping the physical unit of the ability to focus on specific tasks (esp. in higher states of consciousness) and by facilitating easy external behavioral control (i.e. manipulation by others). Because physical units that lack mental control are easy to control, mental control is discouraged in working class educational streams.
Psychedelic tripping, inability to focus, short attention span (something encouraged by our growing daily dependence on "devices"), and brain disorders like Obsessive Compulsive Disorder (OCD) are all exams of lack of mental control.
Mental control is is established through a simple act of will.