Assurance is never absolute because it provides "reasonable," not "absolute," confidence. This is due to the inherent limitations and fallibility present in every aspect of the assurance process. The systems and controls being evaluated (the subject matter) can have undiscovered flaws. The people producing the information may make errors or engage in fraud. The assurance providers (e.g., auditors) use techniques like sampling and are subject to errors in judgment. Finally, the consumers of the assurance report can misinterpret the findings. This universal potential for error and imperfection makes absolute certainty impossible.

A. Assurance principles and practices are applicable across all industries and sectors, not limited to specific ones. The nature of the assurance work changes, but the concept is universal.

C. This describes a characteristic or outcome of assurance not being absolute, rather than the underlying reason for it. A guarantee cannot be provided because of the inherent fallibility.

D. While professional judgment is a critical component, assurance is not solely based on opinion. It is a systematic process that relies on verifiable evidence, testing, and established criteria.

1. OCEG GRC Capability Model 3.0 ("The Red Book"). In the section discussing the design and implementation of controls, it states, "It is important to remember that no system of internal control can provide absolute assurance that objectives will be achieved. Inherent limitations exist, including the possibility of faulty human judgment, management override of controls, and collusion to circumvent controls." (OCEG, GRC Capability Model 3.0, 2015, p. 102). These limitations directly support the concept of fallibility in option B.

2. International Auditing and Assurance Standards Board (IAASB). As taught in university auditing courses, ISA 200, "Overall Objectives of the Independent Auditor and the Conduct of an Audit in Accordance with International Standards on Auditing," states that an auditor obtains reasonable assurance, which is a high, but not absolute, level of assurance. This is because of inherent limitations of an audit, which include the nature of financial reporting, the nature of audit procedures, and the need for the audit to be conducted within a reasonable period of time and at a reasonable cost. (ISA 200, Paragraphs A47-A52). This directly relates to the fallibility of the subject matter and the assurance provider.