One argument that might be made is that inconsistencies at the quantum level create an element of randomness that, while miniscule, could create massive cascading butterfly effects over the course of a large enough timespan. Whether those inconsistencies are enough to make more than a minimal difference in a single given lifespan is debatable at best, and the entire idea could be debunked if quantum physics was proven to be deterministic.
However, as it stands, we don't have accurate methods of predicting quantum behavior.