Cycles to failure. Weak area cycled all night continually separating wood fibers and just on verge of failing. Add some extra water weight from saturated ground all night and she finally fails. Easier to conceptualize when visible defect present and obvious cycling occurring (like wind). Harder to conceptualize when defect may be at molecular level, cycling is not currently present, and stressor is not easily visible.Tree across the street from me survives a nighttime storm. On the following calm, sunny morning, a third of the tree splits off and falls on a car.