Tantalus found a way to properly piss off the Greek gods. It was known gossip that he was asked to join the gods for dinner. Zeus was his father and that helped get him the invite. While he was there he misbehaved. He misbehaved something proper. Some say he tried to bring back the nectar of the gods to the mortals, or that he stole something during his visit. Others say that he served up a main course of his son (boiled) to the gods in a sadistic attempt at an offering. The gods weren’t having it.
He was cast away to the Underworld, Tartarus to be specific, to be eternally tantalized. They set him in a pool, water covering him up to his chin. Above him draped groves of luscious fruit. When Tantalus would bend down to drink the water, the water would drain. When he reached up to grab the fruit, the branches would raise beyond his arm’s length. Suffering continual deprivation while being constantly taunted with nourishment.
Tantalus never stops reaching.