Lennon and McCartney first stated playing together in 1957. By the time they had their first burst of success in 1964 they had performed live an estimated twelve hundred times. Most bands today don’t perform twelve hundred times in their entire careers.
— Malcom Gladwell, Outliers

Repetition: Sir John Eccles found that repetitive stimulation of nerves going to the "spinal cord" led to an increase in the size of the electrical response elicited in “postsynaptic neurons” in the spinal cord. (LeDoux, 137)

Repetition is critical to most types of learning in most cases. People learn by repeating things. They learn by being repeatedly exposed to information, or by repeatedly making an effort to try out a movement, or to find their way from point A to point B. (Pasupathi, Lecture 14) Once information is remembered correctly, it still needs to be reviewed on a regular basis, but at gradually lengthening intervals. This repetition results in reinforcement of the neuronal connections along the lengths of “axons” and “dendrites” and across the “synapses.” The more the neural connections are activated by the stimulation that practice brings, the more dendrites grow to strengthen the connections between the neurons. When the brain perceives information repeated in multiple ways, there is a “priming” process that makes “encoding” of that information more efficient. (Willis, 29)

Repetition Biology: an animal will remember an event (a “stimulus”) as a function of the number of repetitions (of the event). If you give one stimulus, you have a “short-term memory.” If you give five trainings or more, you produce a “long-term memory.” (Kandel Brain and Mind, 5) If you stimulate repeatedly, you release more “serotonin” and that activates “genes” in the “sensory neurons,” which ultimately give rise to the growth of new "synaptic connections." This step requires new “protein synthesis.” (Kandel Brain and Mind, 6)

Repetition Drivers: practice. Practice makes perfect, just as your mother taught you. (Kandel Brain and Mind, 4)

Elaborative Rehearsal: rehearsal that links new information with existing memories and knowledge. (Coon, 301) Rehearsal that involves focusing on the meaning of information to help “encode” and transfer it to “long-term memory.” With elaborative rehearsal, you relate the information to other information you already know. (Hockenbury, 225) Detailed elaboration of our impressions. Thinking or talking about an event immediately after it has occurred enhances memory for that event. (Medina, 131)

Maintenance Rehearsal: the mental or verbal repetition of information in order to maintain it beyond the usual duration of short-term memory. (Hockenbury, 222) You can hold about 7 pieces of declarative information in your head for about 30 seconds. If you don’t repeat it, all of that information goes away. If you do repeat it, it can go into another buffer, which we sometimes refer to as “working memory,” and there it will hold stable for anywhere between 90 to 120 minutes.  If you don’t repeat it then, the information is once again lost and you’re never going to get it back. But if you do repeat it you can recruit it for long-term storage (long-term memory). (Medina, BSP37)

Repetition Intervals: repeated exposure to information in specifically timed intervals. Provides the most powerful way to fix memory into the brain. (Medina, 132)