David and the Smokies exhibit self-assurance and an air of authority due to their purposeful mission and convictions, while Shay's friends may appear younger in memories of the city as a symbol of their lost innocence.
The self-assurance and air of authority displayed by David and the other Smokies can be explained by their confidence in their mission and belief in what they stand for. This depth of character is reflected in descriptions like David’s thoughtful expression when considering an upcoming battle, as mentioned in the text. Furthermore, the memories of Shay’s friends looking younger when recalling life in the city could symbolize the innocence and naivety they once had before experiencing the realities of their new environment.
As for the SEO keywords, one could highlight the transformation of the characters from their past lives in the city to their current state of wisdom and authority. The dichotomy between these experiences may evoke a level of nostalgia and the semblance of youth in the characters' reminiscences.