The Blockchain Trilemma: Why It Is So Hard to Build a Perfect Blockchain

Bitcoin introduced the world to decentralized ledgers over a decade ago. Since then, thousands of blockchain projects have been launched promising high scalability, defined by high throughput, fast execution, and low costs, without compromising security or decentralization. Despite large-scale investment and vast engineering expertise, no network has managed to deliver on all these attributes simultaneously. This is due to a fundamental constraint at the core of distributed systems design – “the blockchain trilemma”.

The term “blockchain trilemma,” coined by Ethereum co-founder Vitalik Buterin, refers to the near impossibility of combining decentralization, security, and scalability in blockchain design today. While two of these properties can be achieved, this is almost always at the expense of the third. The trilemma is rooted in fundamental realities of how distributed systems operate, which makes trade-offs inevitable. Understanding why this tension exists, and how the industry is attempting to address it, is essential for assessing where blockchain technology stands today and where it is heading.

Decentralization vs Scalability

While decentralization is essential to ensure no single party can dominate decisions or censor transactions, increasing the number of nodes in a network tends to introduce coordination challenges. Given that every participating node must receive, validate and store every transaction, the network's throughput is limited by what the least powerful node can handle. And if you raise hardware requirements to process more transactions faster, you price out smaller participants and end up with fewer, more powerful nodes. That is centralization by another name. This is why Bitcoin intentionally keeps its block size small and its block time slow. It is a feature, not a bug – ensuring an ordinary person with a home computer can still run a full node and participate in consensus. However, this decentralization comes at the cost of scalability.

Security vs Scalability

Security is essential because a blockchain must resist attacks, fraud, and manipulation. In practice, however, faster finality and higher throughput often come from reducing the cost of coordination in consensus, for example by relying on a smaller validator set or stronger assumptions about participants and network conditions. Early EOS is a good illustration: its delegated proof of stake design relied on 21 active block producers, which improved performance relative to more open validator models. The trade-off is that a smaller validator set can be easier to coordinate, pressure, or corrupt, reducing resilience compared with systems that distribute validation more broadly. In that sense, higher speed can come with weaker security assumptions, even if the relationship is not purely mechanical.

Decentralization vs Security

Decentralization and security are distinct qualities that do not always reinforce each other. A blockchain can be widely distributed yet still be vulnerable if its consensus design, fault assumptions, or cryptographic protections are weak. At the same time, some mechanisms that strengthen security, such as high staking requirements or operational complexity for validators, can reduce direct participation and encourage concentration among larger operators. Over time, this can weaken decentralization, although the relationship is not automatic, since some security improvements also help preserve decentralization by making attacks more costly.

The Search for Solutions

In the spirit of pushing boundaries, the blockchain industry has refused to accept the trilemma as an immovable ceiling. Several architectural approaches have emerged that attempt to address the constraint. Layer 2 scaling is viewed as the most pragmatic near-term solution. Here, most transaction activity is moved off the main blockchain (Layer 1), while still anchoring its security to it. Layer 2 networks sit on top of a base chain and batch thousands of transactions together before settling them as a single entry on chain. The leading Layer 2 architecture is rollups and there are two types of rollups. Optimistic rollups assume transactions are valid by default, while ZK-rollups use cryptographic validity proofs to verify batches of transactions. Both approaches dramatically increase throughput and reduce costs while inheriting the security guarantees of the underlying chain. It is worth noting that Ethereum's long-term roadmap is almost entirely rollup-centric.

A second solution, sharding, is a technique borrowed from traditional database engineering. Instead of having every node process every transaction, the network is divided into smaller parallel groups of shards, each responsible for a subset of transactions. Nodes only need to maintain their shard's data, reducing the hardware burden while multiplying overall network capacity. Ethereum has long had sharding on its roadmap, though the approach has evolved over time.

Alternative consensus mechanisms also exist. Proof of Work, Bitcoin's foundational consensus mechanism, is secure but energy-intensive and slow. Proof of Stake replaces computational hashing with economic collateral: Validators stake cryptocurrency as a bond, and dishonest behaviour results in the bond being slashed. This enables faster finality and much lower energy consumption. Ethereum's 2022 transition to Proof of Stake was the largest live migration in blockchain history, reducing energy usage by over 99% and fostering greater scalability without sacrificing decentralization. More exotic mechanisms are continuing to emerge, each making different trade-offs suited to different use cases.

Perhaps the most philosophically interesting response to the trilemma is the idea of modular blockchains separating the different functions of a blockchain (execution, settlement, etc.) into specialized layers that can each be optimized independently. This modular paradigm represents a fundamental shift in thinking: Rather than building one chain that does everything adequately, a stack of specialized chains is created, each excelling at its specific function. With this solution, the trilemma doesn't disappear but is distributed across layers, with each making its own narrow trade-offs so that overall performance surpasses that of any monolithic chain.

Will the Trilemma Ever Be Solved?

Today, the debate continues about whether the trilemma can eventually be solved through advances in cryptography, making it possible to build a blockchain that combines all three properties simultaneously. For example, ZK rollups enable high throughput and strong cryptographic security guarantees while settling on a decentralized base layer, offering a glimpse of what might be possible. However, some observers remain sceptical, noting that every “solution” introduces new assumptions, new attack surfaces, or new forms of centralization in bridge infrastructure, sequencer design, or governance structures. In this view, the trilemma does not disappear but is instead transformed, with similar tensions re emerging at higher levels of abstraction.

Conclusion

The blockchain trilemma represents a genuine engineering challenge that sits at the intersection of distributed systems theory, cryptography and game theory. Every major design decision in the quest to build the perfect blockchain can ultimately be traced back to it. When a new chain promises to be highly scalable, while at the same time being more secure and decentralized than ever before, the first question we must ask is: What was compromised to get there? Let’s not forget that the promise of blockchain censorship-resistance, permissionless access, self-sovereign ownership depends on genuine decentralization. And if the only way to scale is to centralize, then we have effectively built an elaborate infrastructure – only to arrive back where we started. Conversely, a blockchain that is beautifully decentralized but can only handle seven transactions per second will never serve the billions of people who need the financial infrastructure the most. Hence, scalability is not a luxury. It is ultimately a prerequisite for impact on a mass scale.

Against this backdrop, the trilemma is ultimately about the kind of system we want to build and who we want it to serve. It is not just a puzzle for engineers but also has profound implications for how we think about the future of finance, governance and the Internet itself.

About the Author
Article authored by Pascal Hügli, Crypto Investment Manager, Maerki Baumann & Co. AG