I have made my way through 47% of sixth grade math over at the Khan Academy, and now things are slowing down quite a bit. I'm still putting in the same amount of work and time, but my progress is now moving in centimeters rather than in feet or even inches (I have completed 47% of sixth grade math, and from the average number of problems I answer correctly, I would give myself the grade of C so far). In order to show the algorithm that you know a skill, you need to get five problems in a row right. When you can get five problems right, you move further along in your quest towards completing the sixth grade. Each percentage point is hard won at this point.
There is certainly something about being able to do something five times in a row correctly. It is my new yardstick to assure me that I know a difficult passage in a piece of music. If I can repeat something five times in a row correctly (at the arrived-at tempo marking), I could probably repeat it correctly a hundred times.
Perhaps five times IS the charm.
Five times what? You ask.