Immutability

Immutability is the property that once data is recorded on a blockchain and buried under enough later blocks, changing it becomes impractical. The guarantee is economic rather than magical: each block commits to the previous one through a cryptographic hash, so altering an old transaction invalidates every block after it and would require redoing all that work or stake. Nothing physically prevents a rewrite — a network with enough concentrated power can reorganize recent history — but the deeper a transaction sits, the more it costs. Immutability cuts both ways for users. A transfer sent to the wrong address, an approval granted to a malicious contract, or funds sent over the wrong network usually cannot be reversed by anyone, including the project's developers or an exchange.