We’ve probably all heard this little tale in one variation or another. Wikipedia attributes this particular version to DC Comics. I like this version because it includes a Knight in the logistics chain, but I don’t like the last line so I put in the one I prefer.
Overall, I like the thing as a reminder that in fiction writing one should seed in all the little things which combine to make a big event happen, or not happen, and have it be believable.
For want of a nail the shoe was lost,
for want of a shoe the horse was lost,
for want of a horse the knight was lost,
for want of a knight the battle was lost,
for want of a battle the kingdom was lost.
So a kingdom was lost—all for want of a nail.
All for the want of a horseshoe nail.