In this paper we consider some general effects observed at pulse electric breakdown of dielectric gaps and dynamic failure of continuous media. The effect of time and strain rate dependence of limiting characteristics, the substitution effect of maximal strength, as well as failure and breakdown with delay are considered. Despite the different physical nature of mechanical failure and electrical breakdown, these effects can be modeled based on a common approach of the incubation time criterion. It is discussed that the strain/stress rate dependence of strength and the volt-time characteristic of a dielectric medium cannot be used as a universal characteristic of the material's mechanical and dielectric strength and should be determined for each specific case. It is shown that the time parameter, which is invariant to the action history, is more appropriate as a characteristic of the dynamic strength. With the incubation time criterion one can construct a unified time dependence of the mechanical or electrical strength consisting of quasi-static and dynamic regimes of action.