The world has a new space race.

In the past two weeks, teams from Richard Branson’s Virgin Galactic and Jeff Bezos’ Blue Origin launched their respective founders into space, signaling a forthcoming era of commercial space travel. These achievements came on the heels of multiple successes from Elon Musk’s SpaceX, which recently made history as the first private company to send a spacecraft to the International Space Station.

Each company has taken a different approach to designing their rockets and shuttles. What they’ve all done, however, is deviate from the tested blueprint NASA has used for sixty years.

If you’ve ever seen a NASA rocket launch, you’ve likely noticed most spacecrafts have two side boosters that lift them into the atmosphere. These rockets are called solid rocket boosters, or SRBs.

The engineers who built the SRBs initially wanted them to be wider to create more thrust. The reason these SRBs are so narrow might surprise you and provide a valuable lesson.

As it turns out, SRBs are a specific width because NASA transports them by train from factories to launch sites. They were initially designed to be narrow enough to fit through American railway tunnels, which are designed to be just a bit wider than the rails themselves.

This might lead you to wonder why American railway tracks are spaced exactly 56.5 inches apart. The answer to that question is surprisingly straightforward: each set of rails is spaced according to a standard railway gauge first used centuries ago in England.

When Americans first decided to build their own railroads, it was only logical to emulate the railways from England so that they could take advantage of many of the same materials and knowledge.

However, this prompts yet another question: how did the English determine this to be the ideal width for a railroad in the first place? Turns out, the English railways were first built with the same tools used to build wagons, which were, in turn, specifically designed to fit the older English roads built by the Roman Empire.

During the Roman Empire, the roads were designed to accommodate the dominant transportation mode of the day, which was a carriage pulled by two horses. Those roads were designed to accommodate the widest part of the horses: their rears.

The moral of this story is that the way the Romans built their roads centuries ago likely had a direct impact on the way we sent humans into space for decades. I’m guessing that while many people probably argued that this is simply the best way to build rockets, others questioned why, and began to think of an entirely new solution and design.

This story is also a good reminder of how inertia tends to take over when a process is working. If something is getting the job done, we are often slow to step off the treadmill, rethink our methods and consider if there is a better way. Unfortunately, we mostly take this step only once the old way stops working altogether.

The fact is, many of our modern inventions and processes are designed based on the way things were done hundreds or thousands of years ago, for reasons we no longer even understand. Knowing this, we should really ask why much more often than we do.

Sometimes we are afraid to suggest something new because we don’t want to stick our neck out only to get hit by the railway tunnel. The next time you need the push to challenge the status quo, remember that one of the biggest limitations on our space program for years was literally a horse’s ass.