In the 1990s, Anders Ericsson, a world-renowned psychologist, studied the students of a music academy in Berlin. The research focused on what factors differentiated the best musicians from the good or the mediocre ones.
After dividing the students into three groups according to their performance abilities, he let them fill out questionnaires about music-related activities. Most students, regardless of group, started playing the violin at the age of about eight, and the time spent on the music curriculum was similar. There was no statistically significant difference.
However, the difference in performance skill was in the invisible part. The group of best students spent an average of three times more time practicing alone than other group students. Deliberate practice during their personal time has made a big difference in skill.
Practice is to repeat the same thing, which is difficult and tedious. However, it is the surest way to do well in your favorite field.