The trade-offs

The trilemma is not an abstract claim — it follows from concrete mechanisms. Each pair of axes pulls against the other in both directions, which is what makes a single optimum impossible.

Decentralization vs. security

One way to increase decentralization is to reduce the number of consensus rounds. This opens longer attack windows and hampers the rollout of patches.

Blockchains often behave according to the weakest link principle: weaker nodes — for example, resource-poor ones — may perform worse as decentralization grows, which also means attacks are noticed later.

Conversely, security is increased by employing modern, more demanding algorithms. Those can reduce the range of usable hardware, so that not everyone is able to participate as a validation node any more — which lowers decentralization.

Decentralization vs. scalability

Maximizing decentralization by involving more validation nodes means that far more communication is required. The larger the workload becomes, the more the network is throttled, and scalability drops.

Scalability is increased, for instance, by using fewer validation nodes, which lowers the network overhead. That makes larger workloads manageable, but it also means the blockchain system depends on only a handful of nodes — making it less decentralized.

Scalability vs. security

Scaling by reducing the number of validation nodes makes it more likely that validation nodes can be compromised, hit by DDoS attacks, or organized as a malicious coalition — all of which significantly affect security.

Conversely, increasing security through resource-intensive processes reduces scalability, because transactions may require longer computation time.