How come the ISO on the Nkin d3000 gets worse the higher it becomes?

I have seen pictures taken by the Nikon d3000 with the ISO at a high number and the pictures look really grainy, how come?

Will it not take good pictures then?

High ISO means that you have fast film speed, which means the photo didn't have time to collect the image completely, leaving it grainy. High ISO pictures are hard to get good no matter what the camara.

The higher the ISO, the grainier the shot. That is fundamental in digital photography.

Read the following: http://www.digital-photography-school.com/use-a-high-iso-to-create-grainy-shots.

ISO on any digital camera is basically the same as ASA on film. The higher the sensitivity the more "noise" (little white dots) you'll end up with in the photo.

Best settings are 800 and below - actually I keep mine always at 200.It's a little more sensitive than
the standard 100 so I get a little faster shutter and slightly tighter aperture without the noise.

Blame it to Physics. Higher ISO, more grain. That is essential to capture more light. It's not limited to the D3000 or Nikon. It applies to all digital cameras, dSLR or not. It also applies to film.

High ISO values have a purpose. That's for taking pictures in low light. You have to balance your priorities. Sometimes, you just have to get a shot that grain wouldn't matter.