Chapter 7 · What Does a Blockchain Sell?
What is the actual product a chain sells?
- Capabilities practiced
- Protocol LiteracyFinancial Literacy
- Hands on
- Record a chain's gas price at the same time for three days; find the highest and lowest times and explain why.
- AI Lab
- Have AI compare blockspace with a real-world market, then identify where the analogy misleads.
A Real-World Problem
Last month, a transfer to your friend cost a fraction of a yuan. Today, the same amount to the same address costs dozens of yuan.
The amount, distance, data size, wallet, and button are unchanged. Why is the price more than a hundred times higher?
Ask further: who receives this fee?
Banks charge for transfers, and card payments pay issuers and acquirers, with published price lists. On-chain transfers have no price list or customer service number to explain today's high price.
Stranger still, you choose how much to pay. Pay less and wait longer; pay more and move ahead. This resembles an auction rather than buying a service with a fixed price.
What, exactly, are you buying?
Thought Experiment
Shrink the world to a town.
Without newspapers or internet, public matters are carved on a wooden board in the square: land sales, debts, and cattle ownership. Once carved, entries count and cannot be erased.
The board has two hard rules:
- A new board replaces it once a day.
- Each board holds only 100 lines.
Year one: About thirty lines are requested daily. There is spare capacity, so the carver charges one copper coin per line and serves everyone.
Year two: Prosperity brings seventy or eighty daily lines. Capacity usually suffices but sometimes fills. On full days, someone discovers that two coins secure inclusion.
Year three: Riverside land goes to auction. Only bids carved on the board count, and earlier lines have priority on the same board. Six hundred people want lines that day.
The carver realizes they control something previously overlooked: one of a hundred positions, and its place in the order.
They announce that the highest bidders get today's lines, with extra payment for the earliest ones.
The first line sells for four hundred coins. A farmer who merely wants to record a small debt gets no line that day.
Pause: what did those four hundred coins buy? The carver's skill and effort are unchanged.
Your Decision
One day in year four, you have something that must be recorded that day.
You sold a cow to a visiting merchant and received payment. Ownership must transfer today because the merchant leaves tomorrow morning. Without the row, ownership becomes a murky dispute.
There are 1,200 requested lines and 100 positions.
What Happens
The choices differ but all ask how to obtain one of a hundred scarce positions.
Three bundled things are traded, rather than the carver's labor:
- Inclusion: whether your entry appears today
- Order: where it appears
- Persistence: everyone sees it and nobody can erase it
Separate them, then reconsider the opening fee:
| Your intuition | What actually happens |
|---|---|
| I pay to make a transfer | You bid for a position on a fixed-capacity board |
| The carver should set prices | Everyone requesting space jointly determines prices |
| Higher costs caused the higher price | More people wanted space simultaneously |
| I pay a service charge | You participate in an auction |
The first conclusion is that nearly fixed supply and demand rising dozens of times within minutes force volatile prices.
Another easily missed property is that cheap capacity cannot be stockpiled. Yesterday's empty lines cannot serve today. Unused daily lines disappear forever. This resembles airport slots or performance seats more than rice or flour.
Build a Model
Arrange the transaction process in a line:
- Something you want to do
- Wait in the candidate pool
- Selected for this block
- Ordered according to bids
- Written into irreversible state
Analyze the chain as a market:
| Market element | On a chain |
|---|---|
| Product | Limited capacity in a block |
| Seller | Block producers |
| Buyer | Everyone wanting transaction execution |
| Price | The fee each transaction offers |
| Supply | Block capacity multiplied by production frequency, nearly fixed in the short term |
| Demand | Transactions seeking execution simultaneously, highly volatile |
Remember three unusual properties:
- No inventory. Unused capacity vanishes and cannot be bought in advance.
- Sold by resource usage, not transaction count. A complex transaction may occupy dozens of times a simple transfer's resources, making a universal per-transaction price misleading.
- Sellers do not set the price. They select transactions while buyers bid against one another.
Most importantly, the market sells not only computation but a result everyone records and nobody can change.
The same computation on a cloud server costs almost nothing. The on-chain premium buys chapter 3's answer: without an administrator, nobody can edit the row afterward.
Blockspace is expensive because of irreversibility, not raw computation. First ask whether an application needs that property before putting it on-chain.
What It Is Called
The phenomena have names.
A chain's limited capacity within each block: its actual product.
Its quantity is protocol-defined, it cannot be stored, and pricing follows usage rather than transaction count.
The unit measuring a transaction's blockspace and computation usage.
Separate gas quantity, determined by the operation's complexity, from gas price, determined by market bidding. The fee is their product.
When people say gas is expensive today, they usually mean its unit price.
The mechanism where pending transactions compete for limited blockspace.
It has a congestion-responsive base price common to everyone and an additional amount you offer. The former determines approximate cost; the latter determines priority.
The extra amount paid to a producer for earlier ordering.
It corresponds to paying extra for the first lines on the board. It is nearly zero in calm periods and can dominate total fees during launches and liquidations.
A state where pending demand persistently exceeds blockspace supply.
Besides high prices, it produces unpredictable costs and exclusion of low-value uses. The latter motivates subsequent scaling chapters.
Bring it together:
A chain is a market selling Blockspace at Gas prices, with buyers bidding rather than sellers fixing prices.
Users buy inclusion, ordering, and irreversibility.
Hands-on
The output is your own recorded table. Online charts become outdated; firsthand retrieval experience is what you need.
Choose a chain and three fixed times. Use morning, afternoon, and late night in your timezone for three days, making nine observations.
Record time with timezone, base fee, estimated ordinary-transfer cost, and recent block utilization.
Find the most expensive observation and investigate what was happening.
Inspect nearby blocks. Are transactions concentrated in one operation type or repeatedly calling the same address?
Fee spikes nearly always have causes visible in blocks.
Find the cheapest observation and its ratio to the highest.
Would that ratio change your decision on a day when you needed to act?
Complete the table.
| Most expensive moment | Cheapest moment | |
|---|---|---|
| Time with timezone | ||
| Base fee | ||
| Ordinary-transfer total fee | ||
| Block utilization | ||
| What was happening on-chain |
Practice deciding. You owe a friend fifty yuan and also have a deadline-sensitive on-chain task.
Using your observations, explain when you would perform each and why.
This produces your first firsthand dataset in the course. Chapter 23 develops retrieval into a formal skill.
AI Lab
Give AI this task:
Offer three real-world market analogies for blockchain blockspace.
For each, explain:
1. Product, seller, buyer, and price formation
2. Three ways the analogy can mislead
3. A fit score from 1 to 5, explaining deductions
Do not default to toll roads unless you first explain why that analogy is inadequate.After receiving them, find three further mismatches in the best analogy rather than merely selecting it.
This trains a useful capability: understanding where an analogy fails lets you use it safely.
Compare with these common weaknesses:
- Toll roads: Unused lanes do not vanish, and roads provide no irreversibility.
- Bandwidth: Providers usually set prices rather than users bidding.
- Performance seats: Seats can be purchased months in advance; blockspace cannot.
- Airport slots: Closest, but allocated rather than auctioned, and lacking irreversibility.
Every analogy is partly right and partly wrong. That is what makes them dangerous.
Verify these points yourself after using AI
- Check that the analogy explains nearly fixed short-term supply
- Check that it does not portray sellers setting prices instead of buyers bidding
- Check whether the analogous product can be stockpiled or bought in advance; blockspace cannot
- Check for omitted irreversibility, which most real markets lack
- Check that gas quantity and unit price remain separate
- Check dates and sources on every specific number
Real-World Case
A digital collectible launch brings tens of thousands of transactions within the same minute, with everyone raising bids for the same block's positions.
An unrelated ordinary transfer then costs dozens of times normal fees.
The lesson is that your price depends on who competes with you at that moment, not only what you are doing.
Some chains market extremely low fees. Sending meaningless transactions then also costs almost nothing.
These chains have repeatedly struggled to process transactions normally. When price stops filtering, another mechanism filters instead: faster networks, more retries, or proximity to producers.
Queues remain but become speed competitions. Chapter 8 encounters this when comparing chains.
A protocol upgrade changed fee structure so the base portion was burned rather than paid to producers.
Beyond deflation narratives, the key distinction is total user expenditure versus producer revenue.
What a chain earns and what its producers earn become separate questions. Chapter 26 applies the same analysis to protocol revenue.
Market crashes create many liquidatable lending positions. The first liquidator earns the reward.
Bots bid against one another, driving priority fees so high that ordinary users can barely transact.
Blockspace competitors are not all humans. A continuously running, economically optimized program may compete with you. Chapter 27 revisits this in product design.
Change One Variable
Fees fall, the first solution everyone considers.
But copying, storing, and checking data grows tenfold. Slower participants fall behind and leave. Years later, newcomers face too much history to catch up.
Larger capacity's real cost is fewer participants. Chapter 11 examines ways around the trade-off.
During congestion, allocation shifts from price to relationships, bot speed, or randomness.
This may not improve ordinary users' experience. Paying more can secure an urgent task; fixed prices remove even that option.
Queues do not disappear; they change form. This holds across system design.
Supply increases and normal fees decline.
But each verifier must receive, validate, and broadcast the same work in one-tenth the time. Slower networks fall behind and participants are excluded.
The same trade-off returns. Chapter 8 expands it into six comparison dimensions.
The chain becomes a rent-generating asset, with persistent blockspace scarcity and high fees.
More importantly, low-value uses are permanently excluded. Small payments, games, and social applications move elsewhere.
That is the starting point for chapters 11 and 12: demand pushed out by price finds another route.
Takeaway Questions
Choose four of the Eighteen Questions for this chapter.
A chain sells a result everyone records and nobody can change.
Ask whether an application needs it. If not, a server is orders of magnitude cheaper.
Users pay fees, but applications may advance them or include them in other charges.
Identify whose pocket ultimately pays to judge sustainability. Chapter 28 follows this through.
A chain's revenue comes from sold blockspace.
Asking whether it makes money means asking whether enough people will pay for that space. This gets closer to its purpose than technical metrics.
Fees and security-provider rewards usually use the native token.
Zero price removes protection incentives. The chain's security budget is tied to token price. Chapter 8 explains the relationship.
Chapter Check
Supply is nearly fixed while demand can surge within minutes.
Protocol-defined capacity and stable block frequency fix short-term available positions. When transactions multiply, price adjusts.
Also, cost depends on who competes for positions at that moment, not just your own action.
Unused blockspace disappears permanently, and you cannot buy future inclusion in advance.
It resembles airport slots or performance seats more than storable goods. An analogy to inventory-bearing commodities misleads here.
Because buyers want a result everyone records and nobody can later change, not merely computation.
A cloud server is fast and cheap, but its database administrator can change the result. The premium buys chapter 3's answer.
If an application does not need that property, putting it on-chain pays for something unused.
It tells only half the story.
Larger blocks lower fees but raise verification requirements: more data, longer history, and slower participants leaving. Fewer participants weaken the assurance against record changes.
The question is what you exchange, not whether it can be done. Chapters 8 and 11 offer different approaches.
There is no answer key. Check four things:
- Did you explain why demand rose?
- Did you separate gas quantity from gas price?
- Did you identify competitors: humans, bots, or a particular application?
- Did you record the retrieval time?
Without the fourth, the observation cannot be reused six months later. The course repeatedly stresses this habit.
Key idea
A blockchain is an open market for trusted computation and settlement; its product is blockspace.