《明史·志·卷五十七》
探究其缘由，便是因为税使苛细收敛，商人到达的人少，连年税使所供，就是这各关卡不足的数目。 
究厥所由，则以税使苛敛，商至者少，连年税使所供，即此各关不足之数也。 
The reason was that tax collectors levied taxes ruthlessly, resulting in fewer merchants coming to trade. The revenues were actually less than the set amounts.