Scalability and the slowness of Blockchains is a hot topic in the crypto community. Georgio Konstantopoulos (@LoomNetwork) provides a very good introduction to the topic in his Medium artice “ Scalability Tradeoffs: “Why The Ethereum Killer” Hasn’t Arrived Yet ”.
As the title state it, it’s a tradeoff of three system properties, which are influencing the scalability of a Blockchain system. Vitalik Buterin, describes that this Scalability Trilemma as follows here:
"This sounds like there’s some kind of scalability trilemma at play. What is this trilemma and can we break through it?
The trilemma claims that blockchain systems can only at most have two of the following three properties:
Decentralization (defined as the system being able to run in a scenario where each participant only has access to O© resources, i.e. a regular laptop or small VPS)
Scalability (defined as being able to process O(n) > O© transactions)
Security (defined as being secure against attackers with up to O(n) resources)”
So what it expresses is the fact, that in case you want to get higher scalability in a blockchain system you have to sacrifice Security or Decentralisation.
As Georgio states in the article
“Α blockchain that claims to have solved the trilemma has either bent the laws of physics (highly unlikely), or it has discovered a breakthrough method that solves the major blockchain scalability problems that have stumped top mathematicians and computer scientists for the past decade”
The article provides various examples (e.g. Ripple’s XRP) which gain scalability by going in a (semi-) centralized direction.
You can read the full article here