You were incorrect in selecting "plays" because, while plays do involve character development and motivations, they often rely on dialogue and visual performance to convey a character's thoughts and feelings, rather than explicitly accessing a character's inner monologue.
The genre that most often uses the technique of revealing a character's thoughts and motivations is fiction, particularly in the form of novels or short stories. Fiction allows authors to delve deeply into a character's psyche, providing readers with insights into their thoughts, feelings, and internal struggles through various literary devices, such as stream of consciousness, soliloquies, or direct narration.
Example of fiction accessing a character's inner thoughts:
In Marcel Proust's In Search of Lost Time, the narrative often delves into the protagonist's introspection. For instance:
"The real voyage of discovery consists not in seeking new landscapes, but in having new eyes." This thought process reveals the character's motivations for understanding the past and longing for lost time.
In contrast, in a play like Shakespeare's Hamlet, while the character's motivations can be inferred through dialogues (like Hamlet's "To be, or not to be" soliloquy), readers do not access the same depth of continuous inner thought as they do in fiction.
Thus, while all genres can explore character motivations, fiction is most adept at employing techniques that provide direct access to a character's mind.