They say a picture is worth a million words. A movie clip says a billion. This video is courtesy of black belt Roy Dean, who does a good job showing the essence of Jiu-Jitsu.
As you will see from the above video, Jiu-Jitsu mostly happens on the mat. The person who knows how to defend herself on the ground will be in her environment when an attacker is out of his. Taller opponents have a reach advantage when standing up. Heavier opponents can generate a lot of force behind their punches. But all of them are susceptible to being taken to the ground and dominated by a smaller, weaker opponent who knows what to do.
You may also notice from the video that once the space is closed between yourself and the attacker, there is little-to-no room for the attacker to use headbutts, punches, kicks, elbows and knees. In real life, things happen too fast to dodge punches like in Jackie Chan movies. Professional boxers bob and weave, but watch how they will take hundreds--if not thousands--of head shots throughout their careers; and these are professionals.
Jiu-Jitsu might remind you a bit of Judo or Aikido. That's because they are all related. But unlike Judo and Aikido, Brazilian Jiu-Jitsu is a progressive martial art that is open to the scrutiny of real life competition and change. The Gracie family improvised on Judo and Japanese Jiu-Jitsu through continuous sparring and competition. This methodology has helped define what many consider the most practical and realistic self defense system in the world. You can go here for more information about the history of Jiu-Jitsu. The page will open in a new browser window so you won't lose your place here!