On incorrect morals.

For want of a nail, the horseshoe was lost.
For want of a horseshoe, the horse was lost.
For want of a horse, the wagon was lost.
For want of a wagon, the supplies were lost.
For want of supplies, the outpost was lost.
For want of an outpost, the expedition was lost.

This is usually read as a parable about the importance of horseshoe nails.

This is incorrect. This is a parable about the importance of safety factors at all levels of one's supply chain.