Why does audit use reasonable assurance instead of requiring perfect accounting?

Audits are designed to provide reasonable assurance that financial statements are free of material misstatement. Absolute assurance would require unrealistic testing of every transaction, estimate, control, and judgment.

Reasonable assurance still requires serious work. The auditor plans procedures around materiality and risk, gathers sufficient appropriate evidence, evaluates misstatements, and considers whether uncorrected items could matter individually or in aggregate.

The exam trap is thinking reasonable assurance means a weak audit. It does not. It means the audit is risk-based and materiality-based rather than a promise that every small number is perfect.