Theory:

A Tragic Story by William Makepeace Thackeray talks about a sage who lived long ago. He has a pigtail attached to the back of his head. The poem humorously narrates the sage's attempt to change the position of the pigtail, from the back of his head to the front of his face. He tries all things possible, but the poet says he has failed in the attempt.
 
The poem is a satire on how wise men can lack practical knowledge sometimes and act in a way that contradicts all the knowledge that they have acquired throughout their life. It also is a representation of how men can waste time pursuing trivial things that do not actually matter in life.
 
The poem is humorous in that it uses repetition of certain words to show the futility of the sage's actions. Thackeray mocks at a group of people who claim that they gained the supreme knowledge through his poem.
 
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The sage with his pigtail