So, at the end of this story Tantalus gets stuck in a pretty awful situation. The water and fruit he wants so badly is eternally just out of his reach. His punishment may seem a tad extreme, but in a way his predicament can be seen as an allegory for the predicament of all humanity.
Some would say the thing that makes us most human is the fact that we tend to always want what we can't have. We're always "tantalized" by things that are just out or our reach. You could say then that Tantalus represents every one of us. Though he's a criminal of the first degree, we all have something in common with the eternal longing that he feels.