Do We Create Our Own Destiny?

"Star crossed lovers
They say we're not meant to be
'Cause the stars in the sky, and the fashion that they are aligned.
I say if the futures been drawn out there's no point in living.
I wont give up my love so that fate can have its way.

If the stars say that you couldn’t love me,
Are you telling me that you would listen?
If the words make their way from your mouth,
Don’t ask my permission,
All is forgiven."
sKsK - Star Crossed

Besides my deep appreciation for this Scary Kids song, listening to it just a moment ago really "got me thinking". Just about destiny, fate, etc. Does it exist? Who creates it? I believe that God does have a plan for each of us but how flexible is that plan? Is there an A and B version of it? Maybe even a C? How predetermined are things? By living in the here and the now, does that automatically rule out X number of possible endings for my day, my month, my year or even my life? Does it really matter? Let's look at the two main schools of thought.

1.) Destiny exists and your life has already been played out in some supernatural podcast. If this is the case, don't worry about anything then. Life will unfold and all you need to do is concentrate on making others as well as yourself happy.
2.) Nothing is pre-planned and everything is a direct result or consequence if your actions in the present. A little closer to what I personally believe but still pretty far from my relatively moderate stance in this. In the same way as predetermination, your decisions are still dependent on the sure and utter fact that the future is unknown. So in that light, you are still able to maintain a certain level of blissful ignorance.

So both 1.) and 2.) rely on us being blind to potential and far reaching consequences. So in the same fashion, your choices still have a very real effect on others. Whether your life's course is predetermined or not, you're still the one making decisions and those decisions can either hurt or help. Day to day, am I helping or hurting? I think everyone's first response would be of course, helping. But how do I know? How much of other people's lives do you really get to see?

Can you really quantify your impact on another human being?