This is an endlessly fascinating topic. I like to consider both sides and am not sure which option I really believe, but here's something to consider...
When I was 18 (ahem, 18 years ago), I visited a psychic/medium. She was a classic 'fortune teller' if you will, and gave me many prophecies that didn't really make sense at the time. Over the years, at least two thirds of what she told me came true- and it wasn't a matter of self-fulfilling prophecy, as I would only realise months or years down the line that what she'd told me had come true. I have a very strong bullshitometer but this woman was the real deal...now if she could tell me what was going to happen, something like fate must exist to some degree? I did ask her how this works- is our destiny set in stone? She described it like this: imagine the root system of a plant. The tap root is the path a person is most likely to follow, but there are other possibilities (the smaller roots leading off the tap root). The smaller the root, the less likely you are to take that path. So what she prophecises is the 'tap root' path. So in essence, we do have a certain destiny somewhat laid out for us, but it is not set in stone and our own free will can lead in many different directions.