A dishonest client may report little or no profit, or even claim a loss, to avoid sharing return. This is a real concern where reporting and business ethics are weak. The response is stronger audit, account control, client selection and enforceable consequences for misconduct—not abandoning partnership altogether.
For banking practice, the rule must also be workable in accounting and monitoring. The aim is to preserve genuine risk-sharing while using a method that can be audited and applied consistently.