This study explores how Machiavellianism, a manipulative personality trait, fuels malicious insider behavior through the Fraud Triangle’s elements: pressure, opportunity, and rationalization. Analyzing 768 U.S. employees via PLS‑SEM, researchers found Machiavellianism strongly influences all three, with rationalization as the primary driver of unethical intent. The findings highlight rationalization’s role in justifying malicious acts, urging organizations to bolster ethical cultures and accountability to curb insider threats. By linking personality traits to situational factors, the study enhances cybersecurity risk modeling and advocates for behaviorally informed insider threat prevention strategies.