Repetition.

The action of repeating or reiterating something in order to fix or retain it in the memory.  Any of various training exercises or activities which are repeated as part of a series or set.

Of the new details he learned he could only retain a few, and those only by continual repetition.

One aspect of getting better is quantity and repetition gives you that. On set or in class the more you repeat, the more practice you have. Repetition is often boring and tiring.