Lightning is a thing of beauty, a vessel of awesome power. Mostly, lightning is some thing to behold. We marvel at it, and we appreciate it when it presents itself, for rarely is it around for long.
From time to time, tragedy accompanies this natural phenomenon and, out of nowhere, lives are turned upside down by a bolt from the blue. When this happens, we comfort ourselves that lightning never strikes twice in the same place.
It's strange that we're so reassured by this idiom. It is, after all, just a saying.