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Tear Jerker: Gattaca
The scene where Jerome burns himself to death, and his silver medal turns gold, and the key scenes where Vincent triumphs against the odds. It's a hugely bittersweet ending, combined with a few heartrending moments.
What makes it worse is the scene before, where Eugene/Jerome shows Vincent/Jerome all the genetic evidence he's been collecting. Vincent doesn't know why he did all this for him, and he doesn't know that Eugene is planning to kill himself, but he still thanks him.
Eugene: I got the better end of the deal. I only lent you my body. You lent me your dream.