I've been developing a theory for my life called "Decades". Do something for ten years then move on by turning the last decade into a hobby and the new one into

I've been developing a theory for my life called "Decades". Do something for ten years then move on by turning the last decade into a hobby and the new one into a profession. It helps to realize that 5-10 years is the right amount of time for the vaunted 10 to 20,000 hours (50 weeks x 20-40 hours/week x 5-10 years). It helps me set expectations too when deciding what to work on: Is this something I would give five years of my life towards? If I enjoyed it enough would I give ten years or more? That was the best outcome of graduate school for me. I worked for four years to get in and another four years to complete the degree. By the end of my post-doc (another two years) I had an appreciation of difficult problems with unknown boundaries. I also had an understanding of how my life would turn out if I exclusively followed that path. I worry today that the focus on rapid iteration leaves aside the challenge of selecting important problems that can truly sustain us long-term. Projects are hard. Sticking with projects is even harder. For me, that has been a whole new lesson in my thirties as I try to develop technologies even as I learned that lesson during my twenties. I hope my forties can start out to be just as confusing as I slowly get a sense of the challenges around me. If not, I'm afraid I'll stagnate and die from the inside out.