A write-off of a loan occurs when an agency official determines, after all appropriate collection tools have been used, that a debt is uncollectible.
Debts which are determined to not be collected are very small in amount. 
mnli hypothesis: Debts which are determined to not be collected are very small in amount.  premise: A write-off of a loan occurs when an agency official determines, after all appropriate collection tools have been used, that a debt is uncollectible.