Answer:
Used left or right, I get to travel over cobblestone or gravel. Used up, I vie for sweet success, used down, I cause men great duress.
If you break me, I do not stop working. If you touch me, I may be snared. If you lose me, nothing will matter.
It's been around for millions of years, but is never more than a month old. What is it?
Through its wounds, water does run. It once held many but now has none. What is it?
Look into my face and I'm everybody. Scratch my back and I'm nobody.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.