Many people want to be remembered as martyrs or heroes; to have proven their devotion to a person or cause, and many people have and do die for this. Some of their deaths may have been in vain; foolish, impetuous sacrifices of themselves that had no true effect, or some of the deaths may have furthered just causes and strengthened beliefs or saved the day. A deeper, case-specific look must be used to judge the true heroes from suicide martyrs caught in a fit of passion. An example of self-sacrifice arises in A Tale of Two Cities by Charles Dickens when Sydney Carton, an alcoholic leading a generally miserable life, sacrifices himself so the husband of the woman he adores (Lucie Manette) can live. He does this by switching places with Charles Darnay, Lucie's husband, just before Darnay's execution.

Whether the switch was a heroic deed or a foolish one can be debated, or perhaps Carton can be both a hero and a fool.
Carton can easily be seen by the Darnay and Manette families as a hero, he made them all happy, not to mention Carton kept his earlier promise to Lucie that he would die to save someone dear to her. 'For you, and for any dear to you, I would do anything. If my career were of that better kind that there was any opportunity or capacity of sacrifice in it, I would embrace any sacrifice for you and for those dear to you,'; he had earlier promised to Lucie.

Also, it could be considered honorable of Carton to take a death when he could have been devious and gotten closer to Lucie in her mourning by comforting her. Perhaps Carton also valued the lives of others more than his own. Quite a commendable trait, if true.
Just as well, Carton is a bit of a fool. Saving Darnay's life did not alter history or anything momentous. Carton killed himself for no solid cause.

Perhaps Carton died over a boyish infatuation with a beautiful woman he could never have, and he thought the only way to get any admiration from her was in death, rather than for the sake of the lives of Darnay and his children.
After all is said and done, Carton brought happiness to the lives of Darnay, Lucie, their Child, and their families by sacrificing his single life. His dying was a good deed and had positive aftermath, but might have been done more as proof of devotion to Lucie than an actual care for the life of Darnay and his family's feelings aside from Lucie's. Basically, Carton probably died just to prove a point and go out in an honorable way, knowing he would at least be remembered for a few generations as a hero.

Had he not died the way he did, he probably would have died a nobody and a drunkard. He probably knows that Darnay and Lucie would name a child in honor of him, and Carton sees that somewhat as a way of beginning anew. His desire to start his life over again is clearly reflected when he tells Lucie, '…have had unformed ideas of striving afresh, beginning anew, shaking off sloth and sensuality, and fighting out the abandoned fight. A dream, all a dream, that ends in nothing, and leaves the sleeper where he lay down, but I wish you to know that you inspired it.

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So, Carton is a hero and a fool. He has generally good intentions, but they are inspired by his infatuation with Lucie Manette. Carton ended his miserable life and enriched the lives of a family. A good-willed and logical decision, if those were his reasons. Anyone who dies to save others is hard to think of as too much of a fool; even if their motivation was self-centered or stupid, they saved several lives and definitely will be a hero in the eyes of those saved.