Unit 2 · Level 2 · The scaling problem
The blockchain trilemma
Every blockchain juggles three properties: decentralization (many independent nodes share control), security (attacks are ruinously expensive), and scalability (lots of transactions, fast and cheap). The 'blockchain trilemma', a framing popularised by Vitalik Buterin, says pushing hard on one usually strains the others. It's an engineering tension rather than a law of physics, and every chain you'll ever meet is one answer to it.
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What you get asked
What does the blockchain trilemma actually claim?
It's a tension, not a ban. Chains can improve on all fronts, but naive gains in one (say, speed) tend to quietly tax the others.
Match each property to what it really means
Keep these three axes in mind and every scaling debate in crypto suddenly makes sense: they're all arguments about which axis to bend.
A new chain hits huge throughput by running on just ten powerful data-centre nodes. What did it likely trade away?
Ten operators can be pressured, hacked or made to collude far more easily than ten thousand. Speed bought with node count is the classic trilemma trade.
The blockchain trilemma balances decentralization, security and ___.
Decentralization, security, scalability: the three-way tug-of-war behind every chain design you'll study in this league.
Why fight so hard to keep decentralization at all?
A fast chain controlled by a few is just a slow bank. Decentralization is the property the whole experiment exists for, which is why nobody gives it up cheaply. 🐜
The rest of this unit
Why block space is scarce, and why 'just make blocks bigger' started a war.