The process that always involves the movement of materials from inside a cell to outside a cell is exocytosis.

Here's why:

* Exocytosis is the process where a cell releases substances, like hormones, waste products, or neurotransmitters, from inside the cell to the outside environment. This happens through the fusion of vesicles (small membrane-bound sacs) with the cell membrane, releasing their contents into the extracellular space.

* Other processes like diffusion, osmosis, and active transport can involve movement in either direction - into or out of the cell - depending on the concentration gradient or the type of substance being transported.

Let me know if you'd like to know more about exocytosis or other cell processes!