newtonian mechanics - Physical interpretation of time constancy in damped harmonic oscillator

I know that one can mathematically derive and prove that in a damped oscillator (without external driving) the time period of oscillations is a constant. But how can one physically interpret as to why should the time period of oscillations be constant even though there is a resistive medium and decreasing amplitude, meaning the amplitude of oscillations decrease exactly with growing time so as to give a constant time period. How can one explain this absolute miracle physically without the help of equations?