You've been lied to! There is nothing magical about the gym. Going to the gym or running a mile doesn't change you. The only thing that happens in the gym or during your run is the stimulation of biochemical processes; that is, the potential for change. And that potential isn't realized until hours after you leave the gym or end your run. It doesn't matter if you workout for four hours consecutively what you do with the remaining twenty hours of your day will ultimately determine whether your workout was a success or failure.