Pareto vs. Weibull

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In a lecture I had it was mentioned that the Pareto distribution is used to model insurance losses for extreme events. A physics theorist told me that he modelled extreme events in solid state theory using a Weibull distribution. I can look up the distributions in wikipedia, but that doesn't really convey when these distributions are applicable, or if there is an underlying model that they are derived from.
Can somebody shed some light, as to what motivates these two distributions and when they can be applied?