If we all had our druthers we’d receive our rewards for anything we did immediately (I’m sure this would have to work both ways; punishments for our actions would have to be just as immediate).
But that way is easy for anyone: Do something, immediate result. The exact thing that makes discipline difficult is that the rewards are sometimes very far out and it’s not always obvious if they’re coming at all. And most of the time when someone can’t see the reward, they’d rather do nothing (or when they can’t see the punishment, they assume there is none).
Discipline, though, is the differentiating factor in acquiring anything that takes time, patience and faith to have — pretty much all the stuff we value (strong relationships, wealth, high-level skill, wisdom…). How much delayed gratification — discipline — you can handle has a linear relationship to how much of those valuables you will have.