According to this principle, no two electrons in an atom have all the four quantum number same. Hence, in an orbital, more than two electrons are not accommodated. Take an example of first and second electron of helium, i.e.,
(He)2 = 1s2
The value of all quantum numbers is given below:
In helium, two electrons e1 and e2 have same set of all quantum numbers except that of spin quantum number. This principle consider as the foundation of quantum mechanics for explaining the stability of an atom and other various phenomena.