How Does PoS Achieve ‘Economic Finality’?

PoS achieves 'economic finality' by ensuring that any attempt to reverse a transaction would require an attacker to incur a greater economic loss than the potential gain. This is done through the threat of slashing.

Once a block is attested to by a supermajority of stakers, the cost to reverse it (losing their staked assets) is prohibitively high, making the transaction practically irreversible from an economic standpoint.