I think you're getting confused between what a system is doing
(eg the position and momentum of a moving body) and the precision with which you can measure
what its doing (where it is and how fast it's going).
Essentially, the indeterminacy (uncertainty) principle.
It may be possible to predict or deduce those two variables to a high degree of accuracy, but if you try to measure
them then the more accurately you know one of them the less idea you have about the other. In the limit, if you could measure exactly
the position of a moving body you would have absolutely no idea how fast it was going or in which direction. This doesn't mean that either its position or velocity didn't have very precise values, just that you can't accurately measure
It's too near my dinnertime to type out an explanation, have a read