Key won't turn in the ignition

It just happened the other day unexpectedly. The car has been driving and working just fine until the ignition wouldn't turn anymore. Is the lock cylinder the only possible thing that can be wrong with it?

IF the key still works in the other locks(door , trunk , glove box) , then either the cylinder failed or it's binding in the column , but you said turning the wheel doesn't help , so without being there first-hand to inspect it , I'm going with lock cylinder failure.