The CAP theorem states that a distributed system can provide at most of guarantees:
Consistency: Every read returns the most recent write.
Availability: Every request gets a response (not an error).
Partition tolerance: The system works despite network failures between nodes.
You can't avoid partition tolerance in distributed systems. Networks fail. So the real choice is: during a network partition, do you sacrifice consistency or availability?
Banks choose consistency. Social media chooses availability.