Because you like Sugar "Kane" Kowalczyk in Some Like It Hot
For the sake of science, Kurisu Makise will persevere no matter how deep into the dark secrets of the world she finds herself. See them in Steins;Gate.
Herion is Mark Renton's favorite drug. He sniffs it, smokes it, swallows it, sticks it up his arse, and injects it into his veins. See them in Trainspotting.
A wildly brilliant detective, Sherlock Holmes can figure out everything except how to interact with other human beings. See them in Sherlock.
Armin Arlert was wrong. This world hasn't become hell; it's been hell. He just couldn't see it before. See them in Attack on Titan.
Pro: Johan Liebert is handsome and charming. Con: he's also a sociopathic killer. See them in Monster (TV Show).
Connor Walsh is arrogant enough to think he's the smartest guy in the room, and quick-witted enough to prove that he is. See them in How to Get Away with Murder.
Member of the student council, captain of the fencing team, and part-time model, Juri Arisugawa is idolized by everyone around her. See them in Revolutionary Girl Utena.
Eliot Waugh is the unspoken leader of his group of friends at a school for magic. See them in The Magicians.
How is angel Aziraphale supposed to stop the apocalypse when Hell's forces misplaced the Antichrist somewhere? See them in Good Omens: The Nice and Accurate Prophecies of Agnes Nutter, Witch.
No one else in fsociety can hack like Elliot Alderson, but the battles being waged in his head are often more than he can handle. See them in Mr. Robot.