I think part of the idea for the metaphor is that, if you see lightning hit a tree, you shouldn't think it is so rare that it wouldn't hit the tree a second time (as some people then think "lightning never strikes the same place twice")... it is, in fact, so rare to have hit anything at all, that it having hit that tree in the first place is an indication that that tree is acting as some kind of preferential local lightning rod and it is highly likely to hit the same tree again.

https://www.theweathernetwork.com/ca/amp/news/article/can-li...

> Believe it or not, this long-held myth is far from the truth. While the odds of being struck by lightning are low, the chances of lightning striking the same place twice are high. Lightning can, and often will, hit the same spot multiple times.