A Flick of Mother Nature's Eyelashes:

My regular morning walk requires me now to skirt around a humbling sight: the enormous branch of an elm tree, almost a foot in diameter and over forty feet long, has crashed to the ground where I normally cross a parking lot. In falling, that branch snapped off a branch of an adjacent elm tree, eight inches in diameter and a bit smaller. The leaves and branch material fill part of the lot, towering above and around me.
A little inspection shows that the larger branch really did snap off the smaller one, which it must have hit with considerable force. The larger branch may have fallen with no warning when it grew to be just a bit too heavy, for it snapped off at its joint with the trunk. One can see that this joint was rotten and hollow, no longer able to support the branch. There was a squirrel's nest in the hollow, and the squirrel is still trying to live in it, although the nest – ten feet above ground – is now horizontal, uncovered, and exposed to the view of all winged predators.
It appears that no person or car was underneath when the branches suddenly fell. That's nice. People will rarely be in the wrong place when a branch falls, but here's a very brief poem on the subject of ash trees, which are relatively likely to drop the random branch:
Ash hateth
Man and waiteth.