The famous pianist Alfred Cortot, wrote that "Any difficulty, reduced to his elementary cell, will be dissolved".

Five, four or even three notes (which I call cells or micro-cells), extrapolated from the analyzed passage and played first slowly and then faster, represent an aim within anybody’s range.

Besides the simple fragment's repetition, it's useful to study it changing the rhythm and the values proportion: this mental training gets the brain used to giving motoric pulses constantly changing every few seconds and allows us to master the hardest passage in a very short time [...]