system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do Newtonian physics break down at a quantum level?
gpt
It's not so much that they break down, rather it's that Newtonian physics is an approximation of how the world works that is not totally correct, but in many cases is accurate enough to be incredibly useful.  In such circumstances (like the ordinary motion of a baseball), the inaccuracy is so low as to be practically imperceptible, though it is still there.  When things become very small, very large, or very fast, however, the Newtonian model is very inaccurate.