The greatest challenge in assessing emerging risk is insufficient data (B). Emerging risks, by definition, lack historical incidents, loss data, and proven impact metrics, making accurate assessment difficult. CISM emphasizes that uncertainty and data scarcity are inherent challenges in emerging risk management.
Complexity (A) and resource constraints (D) are common issues, but without sufficient data, even skilled analysts and mature processes struggle to estimate likelihood and impact. An outdated strategy (C) affects overall effectiveness but does not specifically hinder impact assessment as much as data scarcity does.
References: ISACA CISM Review Manual (Risk management-emerging risks, uncertainty, and assessment challenges); CISM Exam Content Outline (Domain 1).