Characterization through Imagery in Prose

In the following excerpt, the character Greg is portrayed as someone who is deeply introspective and often lost in thought. He frequently sits by himself in the local café, observing the world around him with a mixture of curiosity and melancholy. One day, he overhears a conversation between two strangers, and their words resonate with his own unarticulated feelings. This moment leads Greg to reflect on his own life choices and his relationships, particularly with his estranged father. What characterization technique does the author primarily use to convey Greg's internal struggles?