Answer:
I make you weak at the worst of all times. I keep you safe, I keep you fine. I make your hands sweat. And your heart grow cold. I visit the weak, but seldom the bold.
I have one, you have one. If you remove the first letter, a bit remains. If you remove the second, bit still remains. If you remove the third, it still remains.
I have one eye. See near and far. I hold the moments you treasure and the things that make you weep.
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What can be measured but not seen?
I am the kind of an ant that's good at math. What am I?