Answer:
It regulates our daily movements, but it feels no interest in our lives. It directs us when to come and go, but does not care if we pay attention. What is it?
Brown I am and much admired; many horses have I tried; tire a horse and worry a man; tell me this riddle if you can.
I work when I play and play when I work.
A kind of weather that comes your way, but add a "D" and it will run away
My first is in wield, sever bones and marrow. My second is in blade, forged in cold steel. My third is in arbalest, and also in arrows. My fourth is in power, plunged through a shield. My fifth is in honor, and also in vows My last will put an end to it all.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.