Alfred von Schlieffen was in charge of the entire German army.
In 1905, it became obvious that Germany would have to go to war with France.
France was a huge military power on one side of Germany.
France’s main ally, Russia, was a huge military power on the other side of Germany.
Von Schlieffen knew Germany couldn’t fight a war against both at the same time.
But von Schlieffen also knew that Russia was so huge, it would take them at least six weeks to mobilise their army.
If he could knock out France in six weeks, he could then use Germany’s full might to knock out Russia.
So he spent ten years planning how to defeat France in six weeks.
Von Schlieffen had 600 trained officers in his elite "general staff".
They decided to use the railway system to move their armies to the front.
Between them, they planned the timetables of 11,000 trains.
Then they planned the marching rate of two million soldiers.
They planned everything down to the last detail.
The Schlieffen Plan took nine years, but it was brilliant.
Belgium was neutral, so France never built fortifications along that border.
The German army would simply march through Belgium unopposed and outflank the French.
But, like all plans, there’s always the unexpected.
In this case, the planners made the mistake planners often make.
They forgot that ordinary people aren’t data.
First, they forgot about the ordinary German people who made up the two-million-man army.
The planners had made their calculations based on marching rates of professional soldiers.
But the conscripts were shopkeepers, factory workers and bank clerks.
They weren’t used to marching like soldiers were.
Their feet got so badly blistered, they could barely walk, much less march 25 miles a day.
Second, the planners forgot about the ordinary Belgian people.
Von Schlieffen planned for Germany to smash though the neutral country unopposed,in two days.
But the Belgians fought back and it took Germany more than two weeks to break through.
To do it, they violated Belgium’s neutrality and committed many outrages.
Third, the planners forgot about the ordinary British people.
They were so horrified by what they saw as the rape of neutral Belgium that public opinion forced Britain to go to war with Germany.
Germany was now fighting a war simultaneously with three huge military powers, not just the one they planned on.
And, instead of being over in six weeks, the war went on for four years.
After which Germany was all but destroyed.
The brilliance of the German planners could have worked if everyone had done exactly what all the data said they would do.
But ordinary people aren’t data, and planners don’t allow for that.
They can’t be predicted like numbers on paper.
The planners forgot what Søren Kierkegaard said: "Life can only be understood backwards, but it must be lived forwards."
Or as Mike Tyson put it: "Everyone’s got a strategy until they get hit."
Dave Trott is the author of Creative Mischief, Predatory Thinking and One Plus One Equals Three.