Why is a system of internal control not able to overcome collusion by employees?

A system of internal control is designed to reduce the risk of errors and fraud, but it may not effectively counteract collusion among employees because colluding individuals can circumvent these controls by working together to bypass security measures. Their combined knowledge and access can enable them to manipulate records, conceal transactions, or override checks and balances that would normally detect individual misconduct. Additionally, collusion creates a false sense of security, as the usual red flags may not be triggered when multiple employees are involved in fraudulent activities. Ultimately, the effectiveness of internal controls relies on the integrity of individuals, which collusion undermines.