When such a terrible accident occurs as the one in Los Yébenes, in Toledo, and previously the one in Adamuz, a commotion and social alarm are produced that are so high that there is a tendency to seek quick answers where there are none. Experts point out that accidents are always multi-causal, and that it is not always easy to find a concrete explanation for them. In any case, two levels must always be distinguished. First, it is necessary to identify the error or the chain of errors that led to the misfortune. And second, to analyze the underlying causes that made the error possible.