Ever wonder why a sudden spike in the price of coffee makes you reach for a tea bag instead? Or why, when everyone starts buying electric scooters, the local shop suddenly runs out of lithium batteries?
It isn't just coincidence. It's economics playing out in your kitchen pantry and on your smartphone screen.
Understanding how one product affects another is the secret to understanding how markets actually breathe. We call these relationships related goods, and once you see the patterns, you can't unsee them. It changes how you shop, how you invest, and how you understand the world around you.
What Are Related Goods?
In the simplest terms, related goods are products that have a "relationship" with one another based on how people consume them. They aren't necessarily part of the same category, but they are tied together by human behavior.
When we talk about demand, we usually look at how the price of one thing changes the demand for another. This usually falls into two buckets: things that work together, and things that compete with each other Surprisingly effective..
Substitutes: The Rivals
Subists are the "either-or" products. If you want a burger but the restaurant is out of beef, you might order a chicken sandwich instead. The chicken sandwich is a substitute.
In economic terms, if the price of beef goes up, the demand for chicken goes up. That said, they are fighting for the same spot in your stomach and your budget. They are direct competitors Surprisingly effective..
Complements: The Partners
Complements are the "better together" products. Think about a printer and ink cartridges. A printer is almost useless without ink, and ink is useless without a printer. They are two halves of a single experience Simple as that..
When the price of printers drops significantly, more people buy printers. And because they have new printers, they suddenly need more ink. The demand for one directly pulls the demand for the other Most people skip this — try not to..
Why It Matters / Why People Care
You might think, "Okay, so I'll buy tea if coffee is too expensive. Why does this matter for the big picture?"
Because understanding these relationships is the difference between a business succeeding and going bankrupt. Still, if you run a company that makes high-end espresso machines, you need to care about the price of coffee beans. If coffee becomes a luxury that nobody can afford, your machine sales are going to tank, no matter how good your engineering is.
It also matters for your personal finances. You're looking at mortgage rates. If you're looking at the housing market, you aren't just looking at house prices. Think about it: if interest rates climb, the demand for houses drops. That's a relationship between two different markets that dictates whether or not you can afford a backyard.
Every time you understand these connections, you stop seeing products in isolation. You start seeing a web of interconnected needs.
How It Works: Examples of Related Goods in Demand
To really get this, we need to look at how these relationships play out in the real world. It’s rarely as simple as "A + B = C." It’s often much more nuanced.
The Substitution Effect in Action
Let's look at the classic example: Butter vs. For decades, these were the poster children for substitutes. Margarine. When the price of dairy went up, margarine sales surged Practical, not theoretical..
But it's not just about food. Look at Streaming Services vs. Movie Theaters.
As the cost of a monthly Netflix subscription becomes a standard household expense, the perceived "value" of a $20 movie ticket changes. If streaming becomes cheap and high-quality, the demand for theater tickets might drop. They are competing for your Friday night entertainment budget Not complicated — just consistent..
Another great example is Gasoline vs. Also, electric Vehicles (EVs). This is a complex one because it's shifting. In practice, historically, gas cars and EVs were substitutes. But if gas prices hit $6 a gallon, people look toward EVs. But as the price of lithium (needed for EV batteries) rises, the "price" of owning an EV effectively goes up, which might actually push people back toward traditional internal combustion engines. It's a constant tug-of-war Simple, but easy to overlook. Still holds up..
The Complementary Effect in Action
Complements are where things get interesting because they create "multiplier effects."
Take Smartphones and Mobile Apps. The smartphone is the hardware, and the apps are the software. As smartphones became cheaper and more ubiquitous, the demand for app development exploded. You can't have one without the other. The hardware drove the software, and the software made the hardware more valuable Turns out it matters..
Quick note before moving on.
Then there's Airplanes and Hotels. Still, these are classic complements in the travel industry. If airline ticket prices plummet because of a new low-cost carrier entering a route, you'll see a massive spike in hotel bookings in that destination city. The flight gets you there, but the hotel is what you actually need to stay there. One drives the other.
The "Hidden" Complements
Sometimes, the relationship isn't obvious. Consider Gaming Consoles and High-Speed Internet. A PlayStation or an Xbox is a piece of hardware. But in the modern era, a console is essentially a gateway to a high-bandwidth internet connection. As gaming becomes more online-centric, the demand for high-speed fiber optic internet grows. They are fundamentally linked.
Common Mistakes / What Most People Get Wrong
Here is the part where most people trip up. They assume that these relationships are static. They think, "If A is a substitute for B, it will always be a substitute for B.
That's simply not true The details matter here..
Ignoring the "Threshold" Effect
A relationship can break if the price moves too far. Here's one way to look at it: if the price of beef becomes so high that people can't afford meat at all, they won't just switch to chicken (a substitute). They might switch to lentils (a different category entirely). The relationship between beef and chicken only exists within a certain price window.
Confusing Correlation with Causation
Just because two things happen at the same time doesn't mean they are related goods.
To give you an idea, you might notice that when sales of sunscreen go up, sales of ice cream also go up. Here's the thing — technically, no. And are they related goods? It's hot. People want to stay cool. And they are both being driven by a third variable: the weather. In real terms, they don't substitute for each other, and they aren't complements. Don't mistake a shared cause for a direct relationship.
Worth pausing on this one.
Overlooking the "Luxury" Factor
Some goods are substitutes only when you are on a budget. If you are a connoisseur of fine wine, a cheap bottle of juice isn't a substitute for a Bordeaux. Here's the thing — the relationship only exists for a specific segment of the market. If you're analyzing demand, you have to ask: Who is the consumer?
Practical Tips / What Actually Works
If you're trying to use this knowledge—whether for business or just to be a smarter consumer—here is what actually works.
- Watch the "Peripherals." If you are looking at a product, don't just look at its price. Look at the price of its complements. If you're buying a printer, check the cost of the ink before you commit. If you're buying a car, look at the insurance and fuel trends.
- Identify your "True" Substitutes. If you're a business owner, don't just look at your direct competitors. Look at anything that competes for your customer's time or disposable income. If you sell premium coffee, your competitor isn't just another coffee shop; it's the energy drink company or the local bakery.
- Look for "Bundled" Value. Since complements drive each other, businesses often use them to win. This is why you see "free" hardware with a subscription service, or "buy one, get one half off" on complementary items. They are trying to artificially create a stronger link between the two goods.
- Anticipate the Shift. If you see a massive drop in the price of a complement (like EVs getting cheaper), prepare for the demand for its related goods (like charging stations) to skyrocket.
FAQ
What is the main difference between a substitute and a complement?
A substitute is a product that can replace another (e.g., Coke vs. Pepsi). A complement is a product that is used alongside another (e.
