On the basis of the relation between the ``reliability-function'' (probability of surviving beyond age N in cycles or t in time) and the ``risk'' of failure (as a function of age), the physical interpretation of the latter can be used to extrapolate the former beyond the range of possible observation. It is shown that the asymptotic distribution of smallest values is compatible with the physical concept of (dynamic or static) fatigue, while the logarithmic-normal distribution is not.