In a nutshell, I tend to believe in destiny being pre-ordained, rather than individuals controlling their own destiny. In other words, there are no coincidences, everything is unfolding exactly as it was supposed to.
The genesis of this idea is that so much of what we are is a function of our birth. If you were born in Finland, you would have a reasonable chance to live past the age of 5, be relatively disease-free, fair-skinned, isolated from the world, but cosmopolitan towards its existence. If you were born in Somalia, you would probably be dead before your 5th birthday, without ever having left your country.
Who your parents are has a huge impact as well. Do they have an inherited medical condition? Are they exceptionally gifted with mathematics? Or were they professional athletes? Did they beat you repeatedly or give you unconditional love?
In other words, so much of who we become is decided by factors we can't control, such as our birth and our parents. So it seems incongruous to me that at some arbitrary point (8 years old, 18 years old, 28 years old?), we suddenly take the wheel of our future and start driving, when so much is already in place by that time.
Another way of looking at it is that our lives are like a book. The story is written, we are just turning the pages until the conclusion. Think again: we are on a train track whose destination we don't know, but is laid out before us to follow.
What we have is, in fact, an illusion of control, where we think we are making our own decisions and striking out on our own path, but really, we are just fulfilling our destiny. It's not plausible in my mind that time would be a straight, unchanging line behind us (the past), but an infinite series of lines in front of us (the future), but then this is something that our brains haven't wrapped themselves around in the first place.
Which is why it is a belief on my part, and I am a long way from saying it's a fact. My viewpoint is that we can't control what will happen to us, it's already pre-ordained. Our test of life is how we choose to react to events in our life. That is where we have our control. Or is that, too, an illusion?
All this to say that those who thought the world would end today (06/06/06 if you keep track of these things) were simply waiting for a destiny that didn't exist, and will not exist today.