The origin of E = mc2 may be understood since days of Newton but qualitatively. If Einstein's September 1905 paper is critically analyzed (with different values of variables) then the feasible result is 'when light energy is emitted by a luminous body its mass must increase', which is a contradiction. The perpetual energy machine is not possible. The reason is that Einstein derived light energy-mass interconversion equation (L = mc2) under special conditions of variables only.