The loan nobody records can remain clear through trust until memory begins disagreeing.

An unwritten loan works perfectly while both people remember it the same way. Memory is not a filing system, though; it edits gently in the direction of each person’s sense of themselves, and after a year the two accounts can differ without anyone lying. What then feels like a question of honesty was only ever a question of record keeping.

Writing something down is not distrust, and it is far easier at the beginning than to raise later. A short message confirming the amount and the rough plan protects the friendship more than it protects the money.