I believe we make our own destiny to a certain extent but there are also many factors which we either cannot control or cannot know about. Life is like taking a trip in the car. Whether we turn right, left or continue straight at any certain intersection we change our path although we may end up at the same final destination.
Our live are full of choices and decisions each one of which could drastically alter our path and even our final destination. There are also many hidden obstacles and even malicious acts of others which could get in our way (or end our life).
The factors and variables are so many that it would be impossible to trace but overall I believe we ourselves hold the biggest power in our futures.