Crypto glossary
Blockchain trilemma
The blockchain trilemma is the idea that a blockchain struggles to be decentralized, secure and scalable at once, and usually sacrifices one of the three.
The concept, popularized by Ethereum co-founder Vitalik Buterin, describes three goals that pull against each other. Decentralization means many independent participants can run nodes on ordinary hardware. Security means attacking the network is very costly. Scalability means handling a large volume of transactions cheaply. Raising block sizes or speeds increases throughput but makes nodes harder to run.
The trilemma frames most debates about design. Bitcoin and Ethereum's base layer favour decentralization and security and accept limited capacity. Some high-throughput layer-1 chains rely on fewer, more powerful validators. Layer 2 rollups, sharding and modular designs are attempts to add scale without giving up the other two properties.
It is a rule of thumb, not a proven law, and its terms are loosely defined, so projects claiming to have solved it deserve scrutiny. The useful question is which property a given chain gives up, and whether that suits its intended use.
Example
A chain that raises its block size tenfold may cut fees, but if running a node now needs 1 TB of fast storage a year, far fewer people will verify it independently.
