Taekwondo training may be compared to playing cards. When you play cards, you use all your skills to play the best game you can, using the cards you are dealt. Depending on the version of the game you are playing, you may improve your hand somewhat by exchanging some of your cards, but basically, you must play with the cards you are dealt. Your fellow players must also play with the cards they are dealt. Sometimes, no matter how well you play your cards, your opponents win; sometimes because they are more skilled at playing poker, sometimes because they were dealt better cards.
In Taekwondo training, you use all your skills to train the best you can, using the cards life has dealt you. Sometimes, no matter how hard you train, some of your fellow students do better than you. This may be because they are more skilled than you are, or it may be because life has dealt them better cards, such as they are naturally taller, stronger, faster, more flexible, etc. You may improve your hand by an extra training effort, but sometimes, life just deals you a bad hand, such as a physical or mental disability, illness, injury, etc.
If you have been dealt a bad hand in life, you have to accept it, since there is little you can do about it. However, you do have a choice in how you play your hand. You can lay your cards down and quit, or you can play the cards to the best of your ability. You may receive much enjoyment from playing Taekwondo without ever winning. The satisfaction comes from knowing you are doing your best.
Taekwondo belt promotions are awarded on how well you perform the required techniques and how much you have improved since the last promotion, with consideration given to the hand life has dealt you. Taekwondo promotions are not just based on how well you play the game, but also on how well you play the game considering the hand life dealt you.