The belt is a subject of much controversy in BJJ, owing much to the lack of formalized standards and consistency from one school to the next and the capricious nature of promotions. Belts are a part of the culture, as is claiming that they shouldn’t be.
A BJJ belt is a wholly subjective evaluation by an imperfect instructor based upon his or her own ideas of what it should mean. Still, we try. It’s better than nothing, and helps a student understand where their skills and abilities stand relative to other students, but more importantly, their old selves.
When you start, you’re a white belt. It takes at least a year, probably more, to achieve the next rank of blue belt. To earn a black belt requires much longer, and less than 10% of those that practice the art will achieve the rank. The belt is never the goal, unless you really want to quit.