Photography means, in essence, to capture a moment in time, using light.
The interesting thing is, though, how long is this moment actually?
A very short moment (=fast or short exposure) can catch water in mid-air, frozen in time. This needs a lot of surrounding light, though, but only a short time-frame. It can usually be done by holding the camera in your hand.
A very long moment (=long exposure) can make the same scene look like something out of a fairy-tale. The same water looks soft, somewhat "milky". This needs less light but a longer time-frame. Ideally there's where you start using a tripod.
The shorter exposure is more common because one needs no extra gear like a tripod.
Because it's more common, it's also thought to be more realistic - Actually, no. Both versions can't be seen with your eyes, only with a camera.
Here two examples:
The first a short, the second a long exposure. Both straight out of the camera, no filters etc.
... But, I can't help myself, so here my personal, cleaned up and adjusted version. In that case, of the long exposure one.