For these types of systems, the resulting motion varies wildly given very small changes in the initial conditions. So, for all practical purposes, you can't make it do the same thing twice, since you will always have some error in your knowledge of the initial conditions and even that small difference (the error) will result in a wildly different result. For the same reason, you can't practically tell what it's going to do either even if you know the equations since tiny error in your knowledge of the initial conditions again yields wildly different results. Stable systems, like the earth's orbit, feature negative feedback for deviations so that small errors are brought back into line making it stable. I think systems like this one are the opposite. I think that's what's going on anyway.