Unlike steak and poultry, tough brisket is often the result of undercooking instead of overcooking. That, paired with too high of a smoker temperature, does not allow enough time for all of the connective tissue to break down. One thing that helps when smoking a brisket flat — when the internal temp of brisket reaches 165°F, wrap it in butcher paper to hold the moisture inside. Also, let the meat rest after cooking so the juices have time to redistribute.