What does the term fatuous imply about a person's behavior?

The term fatuous describes a person whose behavior is marked by a complacent foolishness or a lack of intelligence. It suggests an attitude or demeanor that is self-satisfied yet devoid of critical thinking or genuine insight. When someone is deemed fatuous, it indicates they might be unaware of the absurdity or simplicity of their thinking, often resulting in an obliviousness to more serious or profound considerations. In contrast, the other options reflect characteristics that do not relate to the essence of foolishness; they either embody seriousness, strength, or tranquility, which diverge sharply from the implications of being fatuous. Thus, the correct choice encapsulates the idea of a person being foolish in a way that does not show awareness of their shortcomings.