Whoever writes, develops, invents - in short: creates - anything will make a strange observation sooner or later. The more you do, the better you are. You would think that you only have so and so much to give, but as long as you take care of your health, your brain gets more productive if you demand more creativity. It's much harder to get something out of it after you've been lazy for a time. When Sarah Bernhardt (1844-1923) was asked why she's able to work so hard and still be in great shape, she answered "Life engenders life. Energy creates energy. It is by spending oneself that one becomes rich." It's a miracle.