A story is not a race, although it can seem like you are desperately struggling to get to the end. Nor is it a leisurely stroll, stopping to sniff every flower along the way. You must keep the reader engaged, and that requires good pacing.
Pacing is like the tempo in music: sometimes you move faster and other times slower. The story itself will determine this, and you must write accordingly. A fast pace will wear you out, so I usually reserve it for a shorter work, which is by its nature more of a sprint than a run. Move too slow, and it becomes frustrating, like walking through water that is up to your chest. Every step is a labor.
In longer works, the pace will vary: sometimes it will move slower and then pick up suddenly. This is akin to long distance running. If you move too fast, you will exhaust yourself and not be able to finish. If you move too slow, you will lose the race. In writing, you determine the ebb and flow of the story, moving swiftly without being in a rush.
But just as in a race, once the finish line is near, the story speeds up to the climax. It takes a lot of energy to get there, and you pour it all out to give the reader a satisfying finish. Afterwards, the story goes on just long enough for your breathing to return to normal. You soak it in, like a bottle of cool water, knowing the thrill of accomplishment, having given your all.