Her Majesty the elastic band of the pants!
We are passionately discussing here mainly politicians who supposedly rule the world, forgetting that it was not them, but a small, defective horseshoe that led to the death of an entire kingdom. There was no nail - the horseshoe was gone, The horseshoe disappeared - the horse went lame, The horse went lame - the commander was killed, The cavalry is defeated, the army is fleeing, The enemy enters the city, not sparing prisoners, Because there was no nail in the forge.