The 10,000 hour rule is the amount of time that a skill must be practiced before  competence is achieved.  For example, the best athletes, musicians, artists, and craft-persons must repeat a process for 10,000 hours before having command of it.  This according to M. Gladwell in his 2009 book Outliers.  At a typical work schedule of 40 hours per week for 52 weeks, that’s five years of practice.

Practice doesn’t make perfect, but practice does make permanent.  If you practice something wrong, it doesn’t end up perfect, but it does end up permanent.  Habit is powerful.  Effective training always involves repetitions.

The Train-the-trainer lesson expands on these concepts.