Taxi Driver
*This Review may contain spoilers.
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Taxi Driver(1973) depicts NYC as a lawless place with serious social issues(and it was true at time, according to what I read about), where prostitution and drugs and everything bad was a big thing. Travis is a person without a meaningful life, who tries to help the girl because he lacks in meaning and think that he could make the difference by freeing her from the pimp and this whole system that he profoundly hates(not exactly because he thinks that is really wrong, but because he wants to help the girl to find a meaning of life for himself), but turns out that his life kept the same, as shown in the end of the film.
Overall, extremely good movie that needs to be interpreted well to not into the category of "bigger than life" movies(like Fight Club, that might fall under the wrong interpretation).