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What is the blockchain trilemma?
The blockchain trilemma is the claim that a blockchain built with simple techniques can achieve at most two of three properties: scalability (handling many transactions), decentralization (no dependence on a few powerful operators) and security (resisting attacks). Vitalik Buterin popularized the framing; newer designs try to get all three.
Where people disagree
Supporters treat the trilemma as an engineering problem, not a dead end. Buterin argues the limit binds only 'simple' techniques, and that sharding with random validator sampling lets a chain process far more transactions while each participant still verifies on consumer hardware and an attacker cannot concentrate on one shard.
Critics say the trilemma is a lasting structural flaw. The BIS argues that keeping a permissionless chain secure and decentralized requires congestion and high fees, that busy networks push users to competing chains, and that the resulting fragmentation relies on bridges, which have featured in major hacks and depend on a small number of validators.
What it means for you
The trade-off shows up in what you pay and whom you depend on. A network ordinary users can verify tends to have limited capacity and higher fees when busy; one with very high throughput usually relies on fewer, more powerful operators. Cheaper fees on another chain or layer often come with a different trust assumption, so it pays to know which property was traded.
How it works
Buterin defines scalability as processing more transactions than a single consumer computer can verify. Chains where every participant runs a full node get decentralization and security but not scale; chains run by a small set of nodes get scale and security but not decentralization; separate multi-chain ecosystems get scale and decentralization but not security, because an attacker need only take over one chain. He argues sharding, with randomly sampled validators, can achieve all three. The BIS reads the same constraint as a structural limit: congestion pushes up fees and drives users to competing chains.
Sources: Vitalik Buterin, Why sharding is great: demystifying the technical properties (2021), BIS Annual Economic Report 2022, Chapter III: The future monetary system · checked 4 October 2026
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