You're in it for the belts
Setting out to attain your black belt in any martial art is a monumental task and indeed a legitimate reason. If you maintain focus on advancing to the next level through hard work, dedication, blood, sweat and tears, then eventually you will succeed. However, if you have joined purely for the power of belt promotions, then you will find out quickly that you won't have what it takes to be a genuine black belt. If you have this mentality and find yourself still being promoted, then the problem is not only with you but is also rooted within your instructor. If this is you, then quit before you hurt yourself or others.
You're being abused
It's not uncommon for student's to get injured in class through sparring and self defence drills. In Taekwon-do we kick and punch at people, eventually you will get hit. Accidents do happen as we are still learning. However, if an instructor or fellow student purposely causes you pain, discomfort and/or humiliation after you have repeatedly asked them to stop, then this would be an appropriate time to remove yourself from the environment. Remember, it's OK to tell the instructor or a fellow student to stop. Quitting your instructor may be a good idea if you are given the following excuses:
A good instructor will acknowledge your discomfort, apologize, take accountability for their actions and take proper precautions in the future to ensure your physical safety.
Taekwon-do is also a business. I understand that instructors need to be paid as this may be their livelihood. They are providing a service and understandably need to be compensated for their expertise. Fortunately, Taekwon-do schools are a popular business and prices can be compared. A legitimate school will be upfront and honest with all of their business practices. But buyer beware!
Suspiciously Over Qualified Instructor
Beware of the 'over qualified' instructor. It takes a lifetime to master ONE martial art, so why would you want to invest your time and money in an instructor who claims to be a master of all of them? Taekwon-do schools are a dime a dozen and business owners will try to stand out above the rest. Beware of the instructor who boasts about all of their certificates and the many federations they belong to. If they brag about being a provincial, western, national or even a world champion odds are they may very well be, be aren't we all? A good instructor will be humble and prove their character by how they treat you in class. Rank, certificates and titles are sales tactics. Don't fall for them.