Since weights and resistance training are readily available in prison and prisoners have nothing else to do, they train daily to be physically tough. Prison itself makes them mentally tough, much tougher than any bar bully. With so many "masters" of crime available, some prisoners attain their "black belts" in murder and mayhem. Some become "super predators" that are feared by even the toughest street thug. When these prisoners are released, they look for prey. Most look for the weakest prey, such as women, the elderly, or children. Others do not care what type of prey is available since they do not fear injury or death. You are just a piece of meat to them.
There are many reasons why people study Taekwondo; self-defense is one of those reasons. As a martial artist, you may be able to defend yourself against a drunk at the bar, but do not fool yourself, when you are attacked by a predator, unless you have trained for that moment, you will find your life slowly fading away as you lie in a pool of your own blood.