According to legend, king Minos ruled Athens and forced the Athenians to deliver seven youths and seven maidens every nine years.
They became prey of the Minotaur in the labyrinth
Have I forgotten something?
Theseus travelled to Crete as part of the youths to be sacrificed, but he killed the Minotaur and found his way out of the labyrinth by following a ball of string that he had unravelled behind him.
Exiting then became a simple matter of following the thread backwards towards his freedom.
Theseus sailed back to Athens forgetting in his elation to replace the black sails with white ones as a signal of victory.
His father Aegean who was watching for the returning ships from the Sounio rock saw the black sail, and in despair for what he thought was a failed mission that resulted to the death of his son, ended his life by jumping into the sea.