The most important reason to validate that risk responses have been executed as outlined in the risk response plan is to ensure that the residual risk is at an acceptable level. Residual risk is the risk that remains after applying a risk response. The risk response plan is the document thatdescribes the actions and resources needed to address the risk. Validating the risk response execution is the process of verifying that the risk response actions have been performed as planned, and that they have achieved the desired results. Validating the risk response execution helps to measure and monitor the residual risk, and to ensure that it is within the risk tolerance of the organization and its stakeholders. The other reasons are not as important as ensuring that the residual risk is at an acceptable level, although they may be secondary benefits or outcomes of validating the risk response execution. References = Risk and Information Systems Control Study Manual, Chapter 4, Section 4.3.1, page 4-23.