= Why do multiple electrons occupy the same orbital if electrons repel each other?
That is, two electrons per <atomic orbital>, each with a different <spin (physics)>.
As shown at <Schrödinger equation solution for the helium atom>, they do repel each other, and that affects their measurable energy.
However, this energy is still lower than going up to the next orbital. TODO numbers.
Bibliography:
* https://physics.stackexchange.com/questions/505263/do-electrons-in-the-same-orbital-but-different-spin-feel-each-others-coulomb-re
This changes however at higher orbitals, notably as approximately described by the <aufbau principle>.