Linked from
The 25 pages that link to Electron spin, each with the reason it gives.
Aufbau principleRelated: Opposite spin states allow two electrons to share one spatial orbital.
Fine structureRelated: Its coupling to orbital angular momentum distinguishes fine-structure states.
MagnetismRelated: Electron spin supplies a major source of atomic magnetism.
4f orbitalRelated: Two spin states let each of the seven 4f orbitals hold two electrons.
Polykarp KuschRelated: The electron’s spin gives rise to the magnetic dipole Kusch measured.
Joule-secondRelated: Its angular-momentum values are expressed in joule-seconds.