Due to this, the Kohn-Sham orbital energies ε i differ, in general, from the ionization energies I i by the spectroscopic average of the satellite ionizations (see contribution (2.4.9)) as well as by the contributions from the response potential (see contribution (2.2.3)), with equality only for the highest occupied Kohn-Sham molecular orbital. The "well-behaved" (i.e., orthonormal) Kohn-Sham orbitals are, in no way, the "poor cousins" of the Dyson orbitals, forming a distinctively different set of "optimal" orbitals. Indeed, unlike the Dyson orbitals, the occupied Kohn-Sham orbitals meaningfully accommodate the "electron pairs" of conceptual chemistry, while their energies provide a fair estimate of the potentials of primary ionizations. Furthermore, combined with the virtual Kohn-Sham orbitals and their energies, they form the basis for the successful treatment of electronic excitations in TDDFT (see contribution (2.4.9)).