The 13x4 system is a productivity and self-mastery system developed by Benjamin Franklin in which he practiced one of thirteen pre-chosen virtues per week in four cycles per year (13 weeks 4 times is 52 weeks or 1 year).
This allowed him to focus on specific virtues in short managable bursts instead of focusing on everything all at once, with repetions throughout the year to hone the skills/virtues over time.