Figure shows the cumulative failure probability as a function of the estimated lithium whisker diameter, along with the fitted model parameters. We observe a strong correlation between whisker size and failure probability, as evidenced by the linear relationship and fit in Figure . The strong correlation of lithium whisker size to the failure probability is similar to failure size effects in other fields such as fracture of brittle materials and dielectric breakdown in semiconductor gate oxides . In these fields, the size dependence emerges as a result of defects in the materials which are randomly distributed throughout the sample. The similar statistical relationships observed here suggest that the initiation of lithium intrusions is defect-driven with the mechanism illustrated in Figure . In this proposed mechanism, the diameter of a lithium whisker grows continuously until the whisker interacts with a defect, which consequently initiates intrusion growth. For samples with similar k values, d0 provides a quantitative description of the defect density in the material, with higher d0 indicating a lower defect density, and vice versa. The analysis here could also be re-framed in terms of lithium whisker area at failure instead of diameter, with no loss of generality. With this defect-driven interpretation of the failure statistics, next we quantify how mechanical loading affects the probability of intrusion initiation.