Theseus was raised only by his mother. When he was old enough his mother challenged him to move a rock so he could gather some items. He moved it without a sweat.
Theseus went to find his father, he had some challenges on the way but when he got there he heard of a vicious beast named Minotaur.
Black flags on Theseus's ship
Theseus set a trip to go fight Minotaur. He said if the flags are black on the ship when he comes back that means he was defeated. So Theseus forgot to change the flags he when came back, so his father thought he was defeated so he was so sad that he through himself off of a tower.