This achievement is widely considered to be the most difficult achievement in the game, and perhaps one of the most difficult achievements in any Call of Duty game, as the mission requires the player to get one floor higher through many waves of enemies in one minute. Also, there are no checkpoints, and on Veteran the final enemy must be killed with a headshot (if his leg is shot the player will restart from the checkpoint with the message "True veterans get headshots.").
The key to success is to use Flashbangs accordingly, take precise but quick aim and use cover. Not knowing enemy spawn locations can easily lead to becoming gunned down or ambushed.