Carrot

I am in fact 
But a mule hitched
To the front of 
Something behind me prompted 
By whatever carrot floats 
In front always seen
But never ever gotten 
Such a life being
But a mule used
For one thing and 
Promised another and I 
Suppose that when my 
Strength is gone I 
Will be unhitched and 
Shot from behind having 
Never got the carrot