The auditor is not expected to, and cannot, reduce audit risk to zero, and therefore cannot obtain absolute assurance that the financial statements are free from material misstatement due to fraud or error.
This is because there are inherent limitations of an audit, which result in most of the audit evidence being persuasive rather than conclusive. Following are the inherent imiations of an audit.

Nature of financial reporting: The preparation of financial statements involves judgment by management in applying the requirements of the applicable FRF to the facts and circumstances of the entity — for example, accounting estimates.
Nature of audit procedures:

There is the possibility that management and others may not provide complete information relevant to the preparation and presentation of the financial statements (PPFS).
Fraud may involve sophisticated and carefully organised schemes designed to conceal it.
An audit is not an official investigation into alleged wrongdoing. The auditor does not have special legal powers, such as the power of search.

Timeliness of financial reporting and the balance between benefit and cost: The relevance of information, and thereby its value, tends to diminish over time, and there is a balance to be struck between the reliability of information and its cost.
Future events: The business may cease to exist in future due to change in market conditions, emergence of new business models or due to some adverse events
In the case of certain assertions or subject matters, the potential effects of inherent limitations on the auditor's ability to detect material misstatements are particularly significant. Such assertions or subject matters include:

Fraud, particularly fraud involving senior management or collusion.
The existence and completeness of related party relationships and transactions.
The occurrence of non-compliance with laws and regulations.
Future events or conditions that may cause an entity to cease to continue as a going concern.
Significant - Fraud, RPT, L/R, GC

Please understand that:

Because of the inherent limitations of an audit, there is an unavoidable risk that some material misstatements of the financial statements may not be detected, even though the audit is properly planned and performed as per the SAs.
The subsequent discovery of material misstatements resulting from fraud or error does not by itself indicate a failure to conduct the audit as per the SAs.
However, the inherent limitations of an audit are not a justification for the auditor to be satisfied with less-than-persuasive audit evidence.