Summarise How Blockchain Achieves Trust Without a Central Authority

Blockchain promises trust without a bank or government in the middle, and the explanations usually go straight to the deep end. This summarises the core mechanism: what a block holds, why blocks are chained cryptographically, how consensus works with proof-of-work versus proof-of-stake, and why rewriting history is computationally hopeless. The mechanism, minus the evangelism.

Summarise the core mechanism by which a blockchain distributed ledger achieves trustworthiness without relying on a central authority such as a bank or government. Your summary must cover:

- What a 'block' contains and why blocks are chained together cryptographically
- The role of consensus mechanisms: briefly distinguish proof-of-work from proof-of-stake
- Why altering historical records is computationally prohibitive
- One concrete limitation or attack vector that is often glossed over in popular explanations

Target audience: {AUDIENCE}. Length: 150 to 180 words. Do not use cryptocurrency price speculation or investment language. Focus solely on the underlying distributed systems concepts.