In a quantum system, an electron world is compared with a classical system like the solar system or a habitat; almost every physical law has to be changed. It became clear after that the Doubleslit diffraction plays a crucial role in quantum mechanics. The electron diffraction is shown using ion beam(FIB) milled nano-slits, and it is discussed that the phenomena of wave-particle duality demonstrate that all particles have not only wave but particle properties via double-slit diffraction . The wave function exhibiting features of community electrons instead of individual electron systems was proven after these experiments. Therefore, wave function (symbolised as ψ) is statistical data from a group of quantum mechanics, so it is inappropriate to apply to a sole system.