Zeus brings the hammer of justice down on Tantalus in this story. Whichever version of Tantalus's crime you go with, everybody agrees on his punishment. It really has to suck, right? Being forever tormented by food and water that's just out of reach must be pretty awful. We have to hand it to Judge Zeus, though, this verdict is a creative form of justice. It definitely makes us not want to get on Zeus's bad side. In many ways, this story seems like a warning to other mortals to not cross the gods, and it gets across the idea that there's a divine sense of justice in the universe.
It's easy to interpret Tantalus's horrific payback as symbolic for something that all of us have to deal with in life. His legend is more than just a bedtime story designed to make little Greek kids afraid of rustling Zeus's jimmies. We can also look at his eternity of unfilled desire as an extreme example of a condition that every human person has to deal with, that is, the presence unachievable goals. Sometimes, we want something really badly, but we can't get it, and it sucks. We even know that we can't get it, but that doesn't stop us from trying for the rest of our lives. The difference between Tantalus and us is that we have the chance to control our wants and desires, while Tantalus is stuck with the very impossible-to-avoid needs of hunger and thirst.