Cassandra Consistency Level
Consistency level refers to the number of replicas required, but the number of total replicas that exists is independent of the number of nodes. It is set by your Replication_Strategy. If your strategy for this keyspace only has 2 replicas then there are many situations where a CL of 2 would fail.

For nodes A, B and C

Imagine the data you want has been replicated to A and B.

But only A and C are alive. You can only get one replica even though 2 nodes are alive.