Our memories continue to be processed “off-line” following their formation. We have an increasingly sophisticated understanding of these off-line processes, which lead to the reorganization, enhancement and stabilization of memories. Yet, how these off-line mechanisms are controlled leading to some memories being enhanced over wakefulness, while for others this is delayed until sleep is poorly understood. I will provide converging behavioral and physiological evidence that memories are actively prevented from being processed. For example disrupting brain function, with Transcranial Magnetic Stimulation, permits multiple memories, rather than just one, to be processed off-line. Actively preventing off-line processing may regulate consolidation, and ensure that memories remain unstable for a critical function. Instability of memories, I will show is critical for the generalization of knowledge across different tasks.