What is pure simple harmonic oscillation? Why is it not $100 \%$ possible in practice?

(N/A) Pure simple harmonic oscillation is defined as the motion of a mechanical system where no resistive or internal frictional forces act on the system during its oscillation.
Such an oscillation is an ideal situation. In practice,it is impossible to achieve because any mechanical system oscillates within a medium (like air or liquid),which inevitably introduces resistive forces such as air drag or fluid viscosity. Additionally,internal friction within the components of the system always exists. These forces cause energy dissipation,leading to damping of the oscillations. Therefore,pure simple harmonic motion cannot be executed in reality.