Part 9/17:
The Subjectivity and Security of Chain Finality
They examine how Bitcoin’s longest chain serves as an objective measure of validity, easy to verify, even after long offline periods. In PoS networks, "weak subjectivity" is the issue: validators rely on some degree of trust in social consensus or external checkpoints because chain reorganization becomes easier.
Bitcoin is resilient: attacking requires massive expenditure.
Ethereum (PoS), due to the costless construction of chains, can be forked or re-spun more easily, risking stability especially when validators try to "re-evaluate" which chain is legitimate.