If you ever see a crab walking on land, you will find that, it walks tilted to one side. It’s body is such that it cannot walk straight. This fact is true for all the crabs on earth.
One day a mother-crab was sitting on the bank of a river. Her young son was playing nearby. Suddenly, the mother noticed that, her son was not walking straight rather, he was walking tilting his body sideways.
She got worried and advised her son, “You ought to walk straight, not sideways.”
The young crab retorted, “Mother! Show me, how to walk straight. I will follow your example.”
The mother crab tried her level best to walk straight but could not make it and realized her folly.