What Is the Concept of “Nothing at Stake” and How Does PoS Attempt to Solve It?

The "nothing at stake" problem is a weakness in early Proof-of-Stake (PoS) designs where a validator had no economic disincentive for voting on multiple, conflicting chains. Since the cost of validating was near zero, a rational validator could vote on every possible chain fork to maximize their potential reward, thereby preventing the network from achieving consensus.

Modern PoS systems solve this by implementing "slashing," which imposes a severe economic penalty (loss of staked tokens) on any validator caught signing conflicting blocks, thus making the malicious behavior costly.