The Vibe: A system’s ability to keep working correctly and reach agreement even if up to a certain number of participants are lying, crashing, or trying to cheat.
The Details: Byzantine Fault Tolerance means a distributed network (like a blockchain) can still function and agree on one true version of reality even when some nodes (computers) are faulty or malicious (Byzantine faults). The classic limit is that a system can tolerate up to 1/3 of participants being bad (e.g., in a 100-node network, it survives ~33 liars). Bitcoin achieves BFT through Proof-of-Work (very high cost to attack), Ethereum through Proof-of-Stake, and many newer chains (Solana, Avalanche) use variants like PBFT or Tendermint. Without BFT, any single bad actor could fake transactions or double-spend.
Pro Tip: When comparing blockchains, check their BFT model — stronger BFT (higher fault tolerance, faster finality) usually means more security, but sometimes at the cost of decentralization or speed. Bitcoin has the strongest proven BFT track record.