Laws and principles in physics, each of them should have a fundamental reason why and how it works. Through reviewing the reason in ontological point of view, we can find that the singularity of black hole doesn’t exist and the black hole itself is not the end of a star’s life because it will be blown up eventually. Also, it is interpreted that the Pauli exclusion principle is originated in the spin-spin magnetic interaction of elementary particles such as proton, neutron, electron, etc., those of which are known as fermions. With the interpretation for the exclusion principle and a classical model of proton and neutron, we can explain how the nuclear force arises inside the nucleus, why it is in such short range and attractive, and some properties of nuclear force, which is nothing but a special case of electromagnetic interaction. In the same line of thought, new nuclear model is suggested, which is compatible to both liquid drop model and shell model.