Kelly, it is a generalized expression. Coasting can mean "floating" like a piece of wood in the water of a stream. Or, it can be understood as; "one thing moving on top of another thing, but not with strong physical attachment".
So, if the person's essence is their Mind and its conceptions and perceptions, the person refers to a Dual Nature, in which two levels of Mind are in operation.
The Superficial or External functions follow most social conventions.
It tells the person to nod, to be polite and agreeable.
The deeper or Internal part of the Mind is not always agreement with the Superficial Mentality.
I feel intimately connected with the author. It is a recognition of this "dichotomy"
(two--fold way of being) that is demonstrative of a keen awareness of a genuine self.
Arts and Literature and Science also are full of writings which articulate the spiritual
(or psychological) division in the personality.
Sometimes, benefit can be derived from breaking with convention and social custom.
Sometimes a person can identify more with the Internal self which can be externalized, or show its true expression by Not---Being----So----Nice.
An example would be when a person has "friends" that are always asking for favors.
The conventional person functions like a sheep and says; "Yes." However, the internal self may be tired of doing favors, and they can simply say; "No."
Thus, mental and emotional health are maintained.