In one sense, everything is up to chance: there is no plan, and nothing controlling it.
On the other hand, everything is pre-determined. What people do is applied psychology, which is in turn applied biology, which is chemistry, which is physics. As any physics phenomena will result the same way twice, given the exact same starting situation, what will happen wan be predicted, and therefore, if you had enough information, and were impossibly clever (both to the point of godhood), you could work out the entire future of everything