Life HAS purpose, but it doesn't have to be big. We're not all destined to become the next Mother Theresa, Michael Jackson, or Hitler. We are here to learn, to experience, to grow. And just by living, you are experiencing new things.
It could be that your calling is something more simple and that, since you're already there, you're happy. But many of us feel like something is missing, and for those of us who discovered their purpose but aren't there yet, learning to be effective can work wonders. How can you ever become a great painter/write a book/raise children/start your own business if you never have the time? By becoming better at PE, you can make that time and live life the way you were supposed to