The mind is at its best when actively and immersively engaged in two activities: excellence and learning. The energy generated by performing a complex task at a uniquely high quality is exhilarating. The stimulation created by operating at the edge of your awareness in a topic of interest and value is captivating.
Autopilot creeps in and calls your name more and more through each stage of life. The stimulation of learning keeps you engrossed yet humble. The energy of excellence keeps you attentive yet satisfied. But they will not happen naturally on their own. No, they will slowly and steadily fade unless you activate them.