The Byzantine Proof of Stake

The Byzantine part is important because it means that we can tolerate any type of fault including like maliciously generated faults. There's a lot of consensus algorithms like Raft etc. that are fault tolerant to basically machines being offline. But the Raft algorithm can't tolerate machine maliciously or like cooperating with other machines to try to convince the rest of the network that some other value is true. The trick with something like Bitcoin is that it's actually not a safe or correct system and that there is no guarantee that all the nodes on the network are going to have the exact same view of what's happened.