The doctor Hippocrates, who lived in Greece in the years before Christ, created a thesis based on the four primary elements of the universe—water, earth, fire and air. For him, there were also four types of humor in human beings—one hot, one cold, one humid and one dry.
His hunch wound up establishing, a long time later, four types of people, based on their temperaments: the "sanguineous" type, which is happy, calm and not rancorous; the "choleric" type, which is bossy, impetuous and angry; the "phlegmatic" type, which is level-headed and more rational than emotional; and the type deemed the most common on the planet, the "melancholic," which is pensive, creative, a little pessimistic, resentful and slow to act.
Nowadays, while BJJ seems to have high acceptance among happy and impetuous individuals, the gyms, on the other hand, drive away the melancholic, who are more fragile regarding their temperament. One of the key points of the behavior of these people is the victory of inhibition over excitement, which can result in unhappy or incomplete lives.
It is especially for this weaker type, Hippocrates' melancholics, that Rickson Gracie recommends BJJ. They are the ones, after all, who will make the teachers fulfilled and proud of their work—and the gyms more profitable in the process.
Or, as Rickson deftly summed up in recent interviews:
“The jiu-jitsu teacher needs to get the student who's afraid to go outside and make the person feel comfortable enough to say: 'Sorry; this is my place in the line.' Thanks to weekly jiu-jitsu, the person starts loosening up, being able to express themselves."