Rebuild the missing context
Assume the recipient will not remember every date, promise, or earlier conversation. For a message about how to set rules for borrowing your belongings, use this factual base: name the recurring contact, request, topic, or behavior and the effect it has on you.
Say what needs to happen next
State the decision, information, or practical action you need and include a real deadline only when one exists. State the limit, any acceptable alternative, and what you will do if the pattern continues. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Avoid making urgency into pressure
Do not diagnose your friend, list every past grievance, or threaten public embarrassment. For stalking, threats, coercion, or self-harm concerns, preserve evidence and use appropriate crisis or safety support. Do not make the other person responsible for reducing the discomfort that prompted you to write.