Meditation on "for want of a nail"

You've probably heard this before: I came across it in A Wind in the Door.

For want of a nail the shoe was lost.
For want of a shoe the horse was lost.
For want of a horse the rider was lost.
For want of a rider the message was lost.
For want of a message the battle was lost.
For want of a battle the kingdom was lost.
And all for the want of a horseshoe nail.


(source)

I had some thoughts.

1. First, the progression is important here. Sometimes a seemingly insignificant item has a giant effect right away...