Once upon a time, physicists though everything could be predicted exactly, if you only knew all the data required.
However, with the development of quantum physics, we found out that we can't know everything. We can only describe probability distributions.
Experimentally, Heisenberg found and postulated his uncertainty principle that yes, we can measure the position of an electron.
But the direct consequence is the we've got no clue how fast it is going, so we cannot predict where it will be next.
We don't know why this is, but we have experimental confirmation that it is.