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.
I travel in a gaggle.
Until I am measured, I am not known. Yet, how you miss me when I have flown. What Am I?
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
I walk on 4 legs in the morning, 2 legs at noon, and 3 legs at night. What am I?
Give it food and it will live, give it water and it will die.