Two characters have a difficult relationship not because of their differences, but because of their similarities. This is most commonly seen between parents and children or romantic couples, but there's plenty of room for it in other relationships. This can be a sign of latent (or not-so-latent) self-loathing; the character hates himself, so he also hates people who remind him of himself. Or it can be a matter of certain traits' needing to be complemented rather than mirrored in a relationship: someone who talks all the time and someone who would rather listen are obviously better off with each other than with partners like themselves. See You Remind Me Of X, Hypocritical Humor, You Are What You Hate, Turn Out Like His Father, Evil Parents Want Good Kids, Your Approval Fills Me With Shame, Doppelganger Dating.
- Jo and Laurie from Little Women are one of the most famous examples, although when Jo turns down his proposal she also points out the things that are too different about them (she wouldn't like high society, and he wouldn't like her writing).
- On Seinfeld, Jerry (being a narcissist) falls in love with a woman, played by Janeane Garofalo, because they have so much in common; he gradually realizes (being a self-loathing narcissist) what a mistake this is. He tells Elaine how it ended: they were sitting across from each other at Monk's when they both blurted out, "I hate you," and just like that they went their separate ways, still marveling over how they were always on the same page.
- In Road To Perdition, Michael Sullivan, Jr., feels like The Unfavorite and eventually asks his father straight out if he liked Michael's murdered brother better. His father says that he didn't, and that if he treated them differently, it was because Michael reminded him of himself, and he didn't want his own son to Turn Out Like His Father.
- In the Tortall Universe, Alanna's relationship with Liam doesn't work out because they're such similar people: stubborn and temperamental warriors with Chronic Hero Syndrome who aren't willing to adjust for each other, or for anything. George, the man she marries, is a much more laid-back, humorous type.
- In A Tree Grows In Brooklyn, Francie takes after her mother, Katie -- striking her as ordinary -- while her younger brother Neeley takes after their father, a handsome and loving but unreliable alcoholic. Katie devotes herself to making sure Neeley grows up to be like the man she fell in love with, but without his flaws, leaving Francie to fend for herself. She tries to hide her Parental Favoritism, but Francie understands her mother's motives instinctively.
Hello, Unkown Troper. You'll need to get known to lend a hand here.
Three days must pass before this YKTTW is Launchworthy or Discardable