1. A key challenge in conservation biology is that not all species are equally likely to go extinct when faced with a disturbance. Traditionally, differences in species extinction risk are considered a form of extinction selectivity, a nanrondom process by which species’ extinction risks are associated with their traits. While selectivity clearly contributes to varation in extinction among taxa, it is also clear that rare species are more likely to go extinct than are common species. While obvious, this law of extinction suggests that random chance, operating on species abundance, plays an important role in the extinction process. Unless ecologists and conservation biologists can disentangle random and nonrandom extinction processes, then the prediction and prevention of future extinctions will continue to be an elusive challenge. 2. We suggest that a modified version of a common null model procedure, rarefaction, can be used to disentangle the influence of stochastic species loss from selective nonrandom processes. To this end we applied a rarefaction based null model to three published data sets to characterize the influence of species rarity in driving biodiversity loss following three disturbance events: i) disease-associated bat declines; ii) disease-associated amphibian declines; and iii) habitat loss and invasive species-associated gastropod declines. For each case study, we used rarefaction to generate null expectations of stochastic biodiversity loss and species-specific extinction probabilities. 3. In each of our case studies we find evidence for random and nonrandom (selective) extinctions. Our findings highlight the importance of explicitly considering that some species extinctions are the result of stochastic processes, i.e., bad luck. 4. Policy Implications If there is a first law of extinction, it is that rare species are most likely than common species to go extinct. We suggest that taking this law into account in analyses of extinction risk is critical to the identification of selective extinctions. Our results suggest that rarefaction can be used to identify nonrandom decline, extirpation, and extinction events and provide an important baseline comparison point for future extinction analyses.12-Jul-2019