The natural scientist is concerned with a particular kind of phenomena ... he has to confine himself to that which is reproducible ... I do not claim that the reproducible by itself is more important than the unique. But I do claim that the unique exceeds the treatment by scientific method. Indeed it is the aim of this method to find and test natural laws.
Wolfgang PauliThere can never be two or more equivalent electrons in an atom, for which in a strong field the values of all the quantum numbers n, k1, k2 and m are the same. If an electron is present, for which these quantum numbers (in an external field) have definite values, then this state is 'occupied.'
Wolfgang Pauli