The Schrödinger equation is a multi variable second order partial differential equation. You end up with a “position operator” and a “momentum operator” (momentum is mass times velocity, so we focus on the velocity bit). Because of the way that taking a partial derivative works, you end up applying one you can’t get the other.

Idk that’s probably a terrible explanation (I got a C in that class lol), but it is really cool when you see how the math works.