It takes about 7 years to master something.
If you live to be 88, after age 11, you have 11 opportunities to be great at something.
Such a different way of thinking compared to generations of the past when most people would pick one career and stick with it until retirement. This resonates with me since I feel like once I learn something pretty thoroughly, rather than settle down and keep at it, I usually feel like learning something else, which often means drastically shifting my focus. I'm not sure my cycle is exactly seven years, but I assume people learn slightly faster or slower based on many factors.
(discovered through How to learn how to dance in a year on kottke.org)