A character can want something clearly and still struggle to phrase the request. An unsent message gives you a compact way to explore that gap without adding an explanatory speech to the finished story.
Invent a character who needs to ask a neighbour for a small favour after an awkward disagreement. Write three drafts of the message. In the first, make the request directly. In the second, let the character over-explain. In the third, let them avoid the request almost completely.
Compare what changes: the greeting, the amount of background, the placement of the favour and the imagined obligation placed on the recipient. Keep the situation modest enough that differences in wording remain visible.
You do not have to reproduce any of the messages in the story. Perhaps the exercise reveals that the character is less afraid of refusal than of appearing dependent. Show that through one action or a carefully chosen line in the actual encounter.
Avoid treating the draft as a psychological diagnosis. It is a writing tool for this invented person in this particular situation. Another character could use the same wording for a different reason.
Save the three messages beside the scene and note which insight survived revision. The discarded text has done useful work if it helps the final passage become more specific, even when the reader never sees a phone screen or an unsent sentence.
The accompanying visual is an editorial illustration.