In classic mythology, there is the story of the Sphinx, a monster with the body of a lion and the upper part of a woman.
The Sphinx lay crouched on the top of a rock along the highroad to the city of Thebes, and stopped all travellers passing by, proposing to them a riddle.
Those who failed to answer the riddle correctly were killed.
This is the riddle the Sphinx asked the travellers: "What animal walks on four legs in the morning, two legs during the day, and three legs in the evening?"
This is part of the story of Oedipus, who replied to the Sphinx, "Man, who in childhood creeps on hands and knees, in manhood walks erect, and in old age with the aid of a staff."
Morning, day and night are representative of the stages of life.
The Sphinx was so mortified at the solving of her riddle that she cast herself down from the rock and perished.
You are standing next to three switches. You know these switches belong to three bulbs in a room behind a closed door – the door is tight closed, and heavy which means that it's absolutely impossible to see if any bulb is on or not. All three switches are now in position off.
You can do whatever you want with the switches and when you are finished you open the door and go into the room. While in there you have to tell which switch belongs to which bulb.
How will you do that?
Turn on the first switch and wait for a while.
Turn off the first one and turn on the second.
Go into the room.
One bulb is shining, the second bulb is hot and the third one nothing.