At Proof-of-Stake the "Proof-of-Work" is the value lost by stacking up tokens and not having them being productive otherwise. This value could be around 4% per

At Proof-of-Stake the "Proof-of-Work" is the value lost by stacking up tokens and not having them being productive otherwise. This value could be around 4% per year, same as having them on a safe invest. The good thing is that you have to "work less" (just 4%) but if you are a malicious actor you lose all your stake (100%). In conventional PoS you can only lose what you invest, that is why PoS is so expensive.