Motivation and momentum are one dynamic duo. It's a lot easier to stay motivated than to get motivated again. The same is true for keeping momentum.
Comfortable in your job? Things look rosy? Tempted to ease up on the throttle and coast a little? Pinch yourself.
When I need motivation, I remember a story from Jane Goodall, the naturalist trailblazer and gorilla champion, who told a fable that her mother used to read to her and her sister.
"The mighty eagle is sure he will win, and majestically with those great, strong wings he flies higher and higher. ... Gradually, the other birds get tired and start drifting back to the ground. Finally, even the eagle can go no higher ... but that's all right, because he looks down and sees all the other birds below him.
"That's what he thinks, but hiding in the feathers on his back is a little wren ... and she takes off and flies highest of all."
That's the danger of coasting, not giving it your all.
When you have momentum on your side, keep rolling. You have to learn when not to take a break.
Conversely, you also need to know when trying is utterly useless. Manage your motivation in an energy-efficient way.