The Law of Dependencies is like gravity for production.

Imagine a factory with three steps. Cutting. Printing. Finishing.

Cutting can process 100 jobs a day. Printing can process 60. Finishing can process 80.

How many jobs can the factory produce?

Not 100. Not 80. Not the average of the three.

At best, 60.

Printing cannot pass along work it hasn't finished. Finishing cannot finish jobs that haven't been printed. The factory can only ship as fast as its slowest step.

That should feel almost too obvious to write down.

Most of the ways we manage factories don't behave as though this is obvious.

We still measure Cutting on its own. We notice it is only busy 60% of the time. We work out an hourly cost and conclude the machine is expensive when it sits still. So we keep it busy.

Cutting produces 100.

Printing can still only take 60.

The extra 40 have not increased what the factory can ship. They have increased the pile of work sitting in front of Printing.

That pile is not output. It is work in progress.

I call this the Law of Dependencies.

Not because I've discovered some new law of physics. It's simply a useful name for something so basic we tend to overlook it:

In a dependent system, the performance of the whole cannot be understood by looking at the parts independently.

It's a little like gravity.

You don't need to understand gravity to fall off a ladder. And you don't need to understand dependencies to run a factory.

But your factory will obey them whether you account for them or not.

Real factories are not neat three-step lines. A job might travel through sales, artwork, materials, cutting, printing, finishing, packing and dispatch — with branches, skips and subcontractors along the way.

Materials arrive late. A machine goes down. Artwork waits for a customer to approve it. An urgent job jumps the queue. Two products that look similar can eat very different amounts of time at the same resource.

None of that makes dependency less important. It makes it more important.

Every promise you make to a customer travels through a chain of dependencies. If one link in that chain cannot keep up, the promise is already in trouble — even if every other department is having a good week.

Go back to the three stations. Cutting: 100. Printing: 60. Finishing: 80.

An extra hour of capacity at Cutting might accomplish nothing. Cutting was not what was holding the factory back.

An extra hour at Printing might increase what the whole factory can ship.

Same hour. Very different consequence.

That is worth sitting with before anyone reaches for a new machine, a new person, or a new system.

If an hour isn't equally valuable everywhere on the floor, why do we so often manage as though it is?

None of this is complicated. In fact, that's probably why we miss it.

A factory is a dependent system. What happens in one place affects what can happen somewhere else. And somewhere in that chain there will always be something limiting how much the whole system can produce.

You can measure every machine. You can calculate the efficiency of every department. You can keep everybody busy.

But none of those things changes the dependency.

That's why I think of it a little like gravity. You don't have to manage according to it. But you don't get to opt out of it either.

And once you accept that, some of the things we've been taught about efficiency, costing and production management start to look very different.