Let's say you're watching a fast moving object. First it's here [X ]. Then it's here [ X]. If you're playing a video game and it moves that distance between frames, that's what you'll see. If you're watching a movie, you'll see something more like this [XXXXXX ] followed by [ XXXXXX] because there's motion blur. That's why a 24fps movie will seem much smoother than 24fps video game. It's because it's capturing the motion blur.

Now video games could simulate motion blur, but it's computationally expensive, and easier to just make many more frames and let your eyes/brain fill in the blur.