A Goal's End?

When you set goals for yourself, do you see a finish line? Or do you see check points that continue perpetually? I'm curious, I really do want to know. If you're answer is more resonant to the first option, my question would then be "why". Why do you want yourself to stop doing something that you worked so hard to achieve in the first place? For instance, if your goal in life is to be a supreme athlete and you take up a sport, any sport, to achieve that goal, why do you wish to one day stop doing it? I'm not talking about retirement, no. I'm talking about quitting because you've had enough. I'm not judging here, at any place, and I'm only curious why someone would dedicate their life to something, only to be able to no longer do it by choice, at any capacity. I'm only curious and I will never judge, just trying to learn more facets of life that I can not perceive with just my own mind and imagination.

Love, peace.