You can create a marble run and have marbles more or less follow the exact same path every time. However, on some scale there is an unpredictable nature to thin

You can create a marble run and have marbles more or less follow the exact same path every time. However, on some scale there is an unpredictable nature to things like Brownian motion which affect the run in subtle ways. Perhaps you could get closer if you could account for the physical properties of every particle in the system beforehand, but a some scale these interactions are driven by quantum mechanical processes that aren't predictable even with perfect information (as far as we know). To look at it another way, the entropy of a system is always increasing, so you don't have enough information when the marble is at the top of the hill to know the exact outcome when it's at the bottom (on a quantum scale, or over a long enough period of time).