Answer:
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.
Though I am only two words I have thousands of letters in me
You are my brother, but I am not your brother. Who am I?
A dagger thrust at my own heart dictates the way I'm swayed. Left I stand and right I yield to the twisting of the blade. What am I?
I come in different colors and shapes. Some parts of me are curvy, some are straight. I look like I can belong anywhere but there is only one right place for me. What am I?
Give it food and it will live, give it water and it will die.