Fluidity vs. Rigidity

Table of Contents

Fluidity and rigidity show up everywhere once you start looking for them. You can see it in materials, markets, buildings, and in the way people deal with stress. Some things survive by giving a little. Others stay stiff right up until they snap.

The Nature of Fluidity #

A fluid is anything that flows, which includes gasses and liquids. Some fluids even exhibit both properties of solids and liquids, such as in response to shocks (i.e., water with corn starch, a “non-Newtonian fluid”). Ketchup is an example of a substance that does the opposite: it exhibits solid properties until it’s disturbed, after which it flows, which is why shaking or pounding on the bottom of an upturned bottle of ketchup will make it pour out.

Understanding Rigidity #

Rigidity is resistance to flow. To be rigid means you respond to shocks by pushing back, rather than changing shape or getting out of the way. The problem with rigidity is that while it provides the appearance of strength, failures of rigid systems and structures are catastrophic. Properly engineered structures (bridges, buildings, roads, etc.) need to be mostly rigid, but simultaneously provide enough give and take that they don’t explode when a small breeze comes along, or in the event of an extreme shock like an earthquake, avoid total collapse.

The video above shows base isolation: a building stays mostly rigid, but the foundation is allowed to move enough to soak up seismic energy.

Rigidity in Complex Systems #

In markets and economics, we find similar patterns. Rigid financial systems often blow up when exposed to shocks, which sometimes result in bailouts from governments and central banks to protect from so-called “contagion” (i.e., spreading cracks can cause other rigid systems to collapse). The 2008 financial crisis exemplified this, with rigid mortgage-backed securities failing catastrophically when housing prices declined.

The COVID-19 pandemic exposed rigid supply chains that collapsed when faced with sudden demand shifts and transportation disruptions. Companies with rigid work policies struggled to adapt to remote operations, while more fluid organizations pivoted quickly. Tesla also had an easier time than many automakers changing course because it controlled more of its supply chain and iterated faster.

Some substances are incredibly rigid, to the point where they become brittle, and may shatter when stressed. Examples of this are glass or hard plastic, which—as you have likely experienced in your life—will shatter when dropped or smashed. It’s possible to harden glass or plastic, but with enough force applied, even the hardest substances will eventually shatter. These substances are still incredibly useful, but we know to carefully handle objects subject to such failures.

The Mathematics of Fluidity: Ergodicity #

To be fluid means to adapt, overcome, diffuse, and take the shape of the container. Ergodicity is the mathematical term for this concept, and it has some fascinating real-life implications.

Ergodicity comes from the Greek words “ergon” (work) and “hodos” (path), essentially meaning “the same path for all.” While it sounds complex, the core idea is surprisingly intuitive: in an ergodic system, the behavior of a single element over a long time resembles the behavior of many elements over a short time.

Imagine a jar filled with gas molecules. You could either:

Track one molecule as it bounces around for an hour, recording all the positions it visits
Take a snapshot of all molecules’ positions at a single moment

In an ergodic system, these two approaches give you essentially the same information about where molecules tend to be found. The time average (one molecule over time) equals the space average (many molecules at once).

In simple terms, proving ergodicity allows us to consider small samples as representative of the whole, which provides an opportunity to obtain results by sampling.

This matters because it tells you when a sample is actually useful. Consider these examples:

Weather forecasting: Instead of waiting 100 years to see if a prediction model works, meteorologists can test it on 100 different regions simultaneously.
Market research: Rather than testing a product on one person for years, companies test it briefly on thousands of people.
Evolution: Nature doesn’t need to test one genetic variation over millions of years—it tests millions of variations simultaneously across populations.

The advantage of fluidity as it relates to ergodicity and life is that you don’t necessarily need to experience the whole of anything in its entirety; a sufficiently sized sample will do. For example, you don’t need to become an Olympic athlete to find out if you’re good enough for the Olympics: you only need to play the sport a few times (or for a few seasons) to see if you’re better or worse than your peers, or to figure out if you even enjoy it.

However, not all systems are ergodic. Non-ergodic systems are those where single instances can have dramatically different outcomes than the average. Think of a casino game where one massive loss can wipe you out completely—the average outcome across many players might be small losses, but your individual path matters enormously. These are systems where rigidity often emerges, as individual elements (people, institutions) try to protect themselves from catastrophic outcomes.

Ergodicity matters when you’re deciding whether a quick sample tells you enough, or whether one bad path can still ruin you.

The Inevitable Failure of Rigid Systems #

Rigid systems will almost always blow up when exposed to unexpected or unplanned shocks. The cure for poorly designed rigid systems is to allow them to blow up, because it makes sure those systems no longer exist, and you’re only left with fluid systems. Failure is nature’s way of getting rid of the bad stuff.

Abraham Wald and the Missing Bullet Holes #

During World War II, the Statistical Research Group (SRG) at Columbia University was tasked with helping the war effort through statistical analysis. Abraham Wald, a brilliant Jewish mathematician who had fled Nazi-occupied Austria, was among their ranks.

One of the problems presented to the SRG was how to better protect bombers from enemy fire. Military officers showed them diagrams of returning aircraft, with bullet holes clustered primarily in the fuselage and wings. Their initial inclination was obvious: reinforce these heavily damaged areas with more armor.

But Wald saw something the officers missed. He realized they were only examining planes that had survived combat and made it back to base. The bullet holes showed where a plane could be hit and still return safely. The areas without damage—primarily the engines and control systems—were the truly vulnerable spots. Planes hit in those areas weren’t returning at all.

This insight led to one of the most famous examples of survivorship bias in history. Wald recommended armoring the areas that showed no bullet holes on the returning planes, contrary to intuition.

The military’s first instinct was to reinforce what they could see: the holes in the planes that made it back. Wald looked at the missing planes instead.

The same mistake shows up all over the place:

Successful entrepreneurs often study business failures, not just successes
Effective medical treatments emerge from understanding why certain patients don’t respond to therapy
Resilient software systems are designed by anticipating failure modes, not just optimizing for normal operation

The rigidity of focusing only on “survivors” leads to deeply flawed systems. The fluid approach of considering the full spectrum of outcomes—including those that never make it back to tell their tale—creates truly resilient designs.

Where Fluid Meets Rigid #

Fluid systems only blow up where they meet the rigid parts, which is typically around joints or interfaces that haven’t been properly designed to cope with stresses. Interestingly, the fluid parts of the system tend to help absorb shocks anyway, which makes tolerances much higher in a partially fluid system, rather than a strictly rigid system. Nature demonstrates this principle repeatedly—consider how trees bend in high winds rather than snap, or how our bodies use fluid-filled joints to absorb impact.

Netflix’s “Chaos Monkey” is built around this idea. It deliberately breaks parts of production so the system has to keep working through failure instead of assuming everything will behave.

Human Adaptation: Rigidity vs. Fluidity #

Rigid people struggle to adapt as the world changes around them, when they experience hardship, or when things don’t go their way. Those who are rigid expect authority to step in and save them, as opposed to learning to help themselves. Rigid people tend not to survive in a world where survival is all that counts.

People who are fluid go with the flow, they understand that nothing lasts forever, they adapt to the world around them, and they fill the container they’re in. Fluid people don’t bother fighting the trends—as much as they may not like them—and they learn to take advantage of opportunities. Those who are fluid understand that success in life is mostly about luck, but that you can increase your luck by working to maximize exposure to opportunities and making asymmetric upside bets where the downside is limited.

Developing Fluid Thinking #

Developing Adaptability #

If you want to become more fluid, put yourself in situations where you have to adjust. Change your routines on purpose. Run small experiments instead of making giant irreversible bets. Pay attention to systems outside your own lane, because the patterns repeat. And after something goes wrong, don’t just grit your teeth and do the same thing harder.

Books like Nassim Taleb’s Antifragile, Carol Dweck’s Mindset, and Peter Senge’s The Fifth Discipline are worth reading if you want to keep pulling on these ideas.

Conclusion: the Dance of Fluidity and Rigidity #

Fluidity and rigidity aren’t abstractions. They show up in whether a bridge holds, whether a company survives a shock, whether a person can adjust when the world stops cooperating. Complete rigidity breaks. Pure fluidity without any structure just sloshes around.

The systems that last usually have both: enough structure to hold together, enough flexibility to bend when they need to.

That balance matters because shocks are normal, not exceptional. Bruce Lee’s “Be water, my friend” still gets at it. Flow around obstacles, adapt to the container, and keep enough force in reserve to wear something down over time.

If you build everything like glass, don’t act surprised when it shatters.