Brazilian Jiu-Jitsu features the highest dropout rates of all martial arts. Rener Gracie knows this fact, and he has an explanation for JJ drop out rates. For starters, Gracie mentions that BJJ is incredibly complex and challenging. 90% of people never make it to blue belt, and then 1% of blue belts advance to become black belts. Such figures are astounding to say the least.
Also, Gracie points out that BJJ is a demoralizing sport. Participants feel great when things are going well, but then BJJ beats them up and humbles them quite often. Jiu-Jitsu is not designed for those with motivation issues after all. Even the most dedicated fighters may give in and quit, too.