push the envelope

From push (“to continually exert oneself in order to achieve a goal”) + the + envelope (“set of limitations within which a technological system can perform safely and effectively”) (compare flight envelope), referring to the boundary line on a graph of an aircraft’s capabilities, especially those of altitude and speed. The term was popularized by the book The Right Stuff (1979) by the American author and journalist Tom Wolfe (1930–2018) about the pilots engaged in United States postwar research with experimental rocket-powered, high-speed aircraft, and the first Project Mercury astronauts selected for the National Aeronautics and Space Administration’s human spaceflight program.