"Push the Envelope" comes from the era of flight-testing. The most famous "envelope pusher" was Chuck Yeager, who flew the X-15 rocket and broke the sound barrier. Many "experts" predicted he would destroy himself and the X-15 upon breaking the sound barrier- but Yeager (as a test pilot)wanted to "push the envelope" of aircraft-jet areodynamics- anyway- that's my LONG explaination...