Phillip Yancey, What's So Amazing About Grace, Zondervan, 1997, p. 35
Benjamin Franklin settled on thirteen virtues, including
He set up a book with a page for each virtue, lining a column in which to record "defects." Choosing a different virtue to work on each week, he daily noted every mistake, starting over every 13 weeks in order to cycle through the list four times a year. For many decades Franklin carried his little book with him, striving for a clean thirteen-week cycle.
As he made progress, he found himself struggling with yet another defect. "There is perhaps no one of natural passions so hard to subdue as pride. Disguise it. Struggle with it. Stifle it. Mortify it as much as one pleases. It is still alive, and will every now and then peep out and show itself even if I could conceive that I had completely overcome it, I should probably be proud of my humility.