Geometrical confinement is relevant to various disciplines, ranging from the natural sciences via the life sciences to the material science field. Confinement effects have far-reaching influences. They shape efficient hydrodynamic flows, deepen the understanding of biological processes, advance carbon capture technologies, and provide new chemical reactivities. So far, much of the research has focused on demonstrating the importance of confinement in physical and chemical systems while neglecting the fundamental principles that govern these effects. Thus, not much is known about how and why exactly confinement effects modulate key physical phenomena, alter reactivities, or change product selectivity and material properties. As a result, essential questions remain unanswered — what are the underlying physical mechanisms at play in confinement, and how do they alter atomic interactions and influence dynamical properties?