Astrology is not partial based on where you are born or what race you belong too, it will give predictions for both a black or a white born in same location...
Yes we are master of our life...but nothing happens in this world without a reason.
As to say to you in scientific words "Every action has equal and opposite reaction".
Thus based on same, certain predictions can be done, as we try to predict what would be an outcome of a jump which is made at XX speed from a ramp of yy degree of inclination carying zz weight. Extrapolate same scientific method of computation with other N factors and you would be able to predict a lot more about human being..after all its a science
Every human being makes 1000s of prediction in his life as part of day to day action. Some may go right some may go wrong. For example if someone throws a ball at your end and you catch it, then its possible because your brain predicted the path of ball and its speed and reacted accordingly to catch a ball. When you drive a car you predict 1000s of things and make your moves to have a safe journey. Think about it ....and they say if there is prediction or not in life