Humans more easily remember or learn items when they are studied a few times over a long period of time (spaced presentation), rather than studied repeatedly in a short period of time.
Hermann EbbinghausNo matter how thoroughly a person may have learned the Greek alphabet, he will never be in a condition to repeat it backwards without further training.
Hermann EbbinghausThe relation of repetitions for learning and for repeating English stanzas needs no amplification. These were learned by heart on the first day with less than half of the repetitions necessary for the shortest of the syllable series.
Hermann Ebbinghaus