Threat-based risk event modeling often involves significant expert judgment: choosing plausible threats, estimating their capability, attack paths, and motivations, and modeling multi-step attack scenarios. According to CRISC, such modeling demands strong justification and documented rationale because assumptions and inputs may be challenged by stakeholders and auditors. Semi-quantitative approaches and ALE calculations also require explanation, but they are generally based on standardized scales, historical data, or accepted formulas. MTBF is an engineering reliability metric, usually based on vendor data or operational history, requiring limited justification from a risk perspective. Threat-based modeling, however, drives critical decisions about controls and investment, and because it can be sensitive to subjective inputs, risk practitioners must carefully justify scenario selection, likelihood estimates, and impact assumptions to maintain credibility and enable informed governance decisions.