A person can cover a lot of ground in the time it takes another to react.
Ever hear of the 21ft rule? Hell we even disscussed a case at the academy of a shooting ruled justified at 30ft.(don't remember the case though)
Just a little tid bit for those who CCW. Any practice done at the 7yrd line and closer should include instinctive style shooting from in close and at the hip. Outstreched arms turn 21ft into 17ft.