Once you begin your martial art journey, there is no end. Those that say: "I used to be a black belt when I was 10", or "I used to practice martial arts when I was young", are no longer martial artists/are not martial artist.
Martial arts is not a sport, like basketball. In basketball, often a basketball players retires. For example Michael Jordon. Jordon only played for a certain time period, then decided to retire. Martial artist do not train for a certain time period then quit/retire. They train till they die. They make martial arts part of their life. You will only see a martial artist stop training (other then rest day) when they are dead. When they are dead the martial arts die with them, like for example Bruce Lee.
Think also about the shaolin monks. They practice martial arts as a part of their life. In fact martial arts to them is life. If they die, their martial arts die as well.
At the moment people can still consider Jet Li as a martial artist. But what happens in 10 years time?
Will Jet Li still be training? Or will he be Dead? IF he stopped training because he no longer has motivation, then he is no longer a martial artist. IF he stopped, because he meets death then that martial art dies with him but his spirit still remains, and will resonate over generation to generation.
Martial artist are also not those people at the gym or, the people who does a workout program at home like P90X, for a specific time period. Like for example when they reach their destination time, they will decide to leave/quit. There is no destination for martial artist. There is only an infinite and continuous journey. That journey is like life.
Martial artist in my opinion has that self motivation to train.They do not need a goal (like become a master/black belt), or an inspiration to motivate them. They are just simply motivated, why? WHY NOT.