Contrasting 2D and 3D in my field (Discrete & Computational Geometry1) is essential. For example, every 2D polygon can be triangulated (with vertex-to-vertex diagonals), but not every 3D polyhedron can be similarly tetrahedralized.
I experience significant push-back when I move to 3D (with undergraduates in the US). Typical student reaction: "Whoa!" (Most have not had Calc III.)
Q. How do you ease the 2D$\rightarrow$3D transition in your teaching?
I use polydrons, but still it's a scary transition for many students. And I have to prepare them for the leap to dimensions $> 3$.
1 Handbook of Discrete and Computational Geometry. Chapman and Hall/CRC, 2017.