The spin state depends on the relative magnitude of Delta (splitting energy) and P (pairing energy). If Delta < P: electrons prefer to occupy higher orbitals rather than pair — high spin (weak field ligands). If Delta > P: electrons prefer to pair in lower orbitals — low spin (strong field ligands). This choice only matters for d4, d5, d6, and d7 configurations. For d1-d3: only one configuration possible (always high spin pattern). For d8-d10: only one configuration possible. Example: [Fe(H2O)6]2+ is high spin d6 ($t2g^4$, $eg^2$, 4 unpaired) while [Fe(CN)6]4- is low spin d6 ($t2g^6$, $eg^0$, 0 unpaired).