I believe that destiny exists, but it requires more explanation than simple "thinks happen for a reason, period." That would not make sense.
I believe in souls. I believe life is for learning.
I believe that whenever you enter some sort of life form, be it as an animal being (human incl) a plant, some inanimate object, or wathever, you have a goal. There is a reason you became what you became.
I believe that there's a path set out before a soul enters a materialistic form of life, and that path coincides with what needs to be learned. I also believe it is extremely difficult to find out what it is that one is going to learn in a lifetime, for it is far beyond any humanly imaginable concept.
I think dreams could in some way be connected to this, but i have not given it enough thought.
This is all just my opinion, of course. The only downside this brings is that i tend to take suicidal people less seriously, since i believe the time of death has already been set, which is why most people end up not succeeding. This is also why people can survive, for example, a fall from a ridiculous heigth.
This is probably the shortest description i can give of what i believe, concerning destiny.