What is expected of internal auditors in regards to due professional care?

According to the IIA’s definition of due professional care, internal auditors are expected to perform assurance services that are needed to achieve the engagement's objectives. This includes considering the cost of assurance in relation to the benefits. The standard does not require auditors to identify all risks or guarantee that all significant risks will be addressed, as absolute assurance in any auditing context is unattainable.

IIA Standard on Due Professional Care.