Theory:

The poem 'A Tragic Story' by William Makepeace Thackeray talks about a sage who wants to change the position of his pigtail. He does not like to have the pigtail dangling behind his back, rather he wants it to be in the front of his face. This shows that humans, in general, are not grateful for the blessings they have in life. They can be upset about trivial things that have gone wrong rather than focussing on the remaining good things. The sage has a very handsome pigtail, but he is worried about its position.
 
The poem is a satire on how learned men can lack practical wisdom too. The society accepts certain men as mentors and blindly follows their principles and ideals without cross-verifying them. They can be harmful, as these learned men themselves could be in possession of half-baked knowledge. The sage has conquered and mastered all the skills but still is unable to understand that the pigtail is attached to the back of his head and it is foolish to try and bring it to the face.
 
The poem is also an emphasis on how people can waste time by pursuing things that are not important and not possible. It is humorously portrayed that Life is short to waste on unnecessary pursuits like these.