Imagine that you had a GPS, but didn't know where you were going. So you just typed "anywhere" into the address field. What would happen? You would probably get some variation of "address not valid." In the same way, you must have a destination for your martial arts journey. Otherwise, you are no better than a car that is burning gas and wasting time searching for an invalid address.
In the martial arts, your destination is the rank which you want to earn. This will vary significantly based on what you want out of your system, so to help you, here are the key milestones in self-defense training. While each system has its own ranking system, the most important ranks typically fall into these four categories:
Instructor: You have internalized the basic techniques of your system to the point where you can do them instinctively. Not only that, but you have adapted these techniques to your body type and personality. You should have enough focus, discipline and integrity that your master can trust you to lead a class of beginner, intermediate, and advanced students without their help.
In most systems, an instructor is a first-degree black belt.
If your primary goal is self-defense, make this your destination.
Chief Instructor: Through constant study, you have gained a thorough understanding of the principles of self-defense. In other words, you don't just know how the techniques work: you know why they work. You should know your system well enough to independently train a student from beginner to instructor level.
In most systems, a chief instructor is a fourth-degree black belt.
If you do the martial arts as a fun hobby, make this your destination.
Master: To become a master, you must be able to consistently apply the principles of self-defense in new and innovative ways. A chief instructor can get away with being book smart, but you must be street smart. This is probably the most fun rank because you get to constantly experiment to discover which techniques work (or don't work) in the modern world. It's also the stage where you can do research to rediscover "forgotten" techniques and decide whether or not to reintegrate them into the system. Additionally, a good master will cross-train in other systems to keep their skills sharp and to "borrow" effective techniques to refine their own style. At this stage, you should be able to run and manage your own martial arts school.
In most systems, a master is a fifth-degree black belt.
If you want to teach the martial arts, or self-defense is an integral part of your career (i.e. you're a cop), this should be your destination.
Grandmaster: The rank of grandmaster cannot be earned. It must be given. Some systems don't even have an official exam for the rank of grandmaster; it is awarded as an honorary title. To receive this rank, you must have dedicated your life to the improvement and spread of the martial arts. You must also have demonstrated the inner principles of the martial arts (i.e. integrity, respect, discipline, selflessness, etc.) through improving your community. As a grandmaster, you understand that your martial arts journey never truly ends. Not only do you continually refine your body and mind, but your heart and spirit as well. When masters of other schools and systems are coming to you for instruction, then you are probably a grandmaster.
In most systems, a grandmaster is a tenth-degree black belt.
If you are so passionate about self-defense that you are willing to dedicate your life to ensuring that your fellow man experiences the benefits of the martial arts, then you will become a grandmaster. Eventually.
It should be noted that, no matter which rank you get, you will still need to practice to keep your skills sharp. This is especially important at the instructor-level/first-degree black belt rank, because you'll be tempted to believe that you know everything and simply quit. However, self-defense is like any other skill: if you don't use it, you lose it. So even if you become a grandmaster, always remember to PRACTICE, PRACTICE, PRACTICE!