A clever one is aware, since the mind presupposes a fairly high degree of awareness in general. As the famous saying goes - "Reason is limited, and stupidity is limitless." Smart is smart because he is aware of his boundaries, usually through communication with others. However, he constantly doubts and makes mistakes about how smart he is.
This is one of the manifestations of the famous "Dunning-Kruger effect": "The most capable (competent) tend to underestimate their abilities. This is due to the fact that if a task seems simple to a person, then he gets the feeling that this task will be simple for everyone else. "
The second manifestation of this effect is the unconsciousness of the non-smart, they are just poorly aware of their intellectual status and tend to Overestimate themselves.
In this case, I am reminded of the statement of Thomas Carlyle. All greatness is unconscious - otherwise it costs little or nothing.