If you accept that the universe
then it would follow that if you knew the current state of the universe you could predict the future.
Now, the universe is a bit big to cram inside your head, or even into a decent sized computer, so you'll never know enough.
Trying to predict the future of the entire universe might be overly ambitious, but do you know enough to predict any event with 100% accuracy? Afraid not...
Let's take a classic example: Tell me all the possible outcomes of a coin toss. You would probably say "Heads or tails" first and then "It may land on end". Enough? No. There is the probability that the coin will disintegrate in mid air, get eaten by a passing wildebeest or any such thing. The probability for any of these events is infinitesimal, but it's still there. Same thing goes for any activity you think you know all the possible outcomes for. You can say "If I drop a rock, it will fall," and you will probably be right, but you're actually simplifying things a little.
This kind of simplification is useful and serves as a model of the universe that is a lot smaller than the real thing. Just don't make the mistake of confusing the model with the reality. It will only lead to the belief in such silly things as randomness and the construction of strange models of reality like religion or atheism.
It's just a case of not knowing enough. No magic involved.