In order for an observed outcome to be predictable to 100% (effectively) at a macroscopic level it need only be predictable to infinitesimally over 50% at a quantum level.
All outcomes are based on random probability. The fact that we observe certain occurrences with a predictability we consider to be 100% is due to the cumulative probability of all components of the entire system.
Allegorically speaking, if there is a 51% probability that a slightly unbalanced coin will land on heads when flipped, the probability of observing a cumulative total of more heads than tails increases with each flip of the coin. At a point, approaching an infinite number of flips, the probability of the cumulative total of more heads than tails effectively equals 100%.
I believe that we humans must think at a quantum level, hence the ability to make unpredictable decisions. With computers, the probability of a predictable outcome approaches 100% because calculations are made instead at an electronic level which is composed of an unimaginably greater number of quantum particles.
Perhaps the old concept of cosmos and chaos (order and randomness) should be replace with one of probability at microscopic (quantum) and macroscopic scales.