Stationary means "not moving". Stationary sounds like stationery. Stationery refers to paper that is used for writing letters that usually has matching envelopes. No matter how much you "push the envelope" which means to extend the limits of what is possible, it will still be stationary, or unmoving. We see stationery written in place of stationary because they sound the same, except stationery refers to paper with matching envelopes.
No matter how much you push the envelope , it ' ll still be stationery .