There are few things as deadly and unpredictable as curiosity. However, what's most dangerous about curiosity is its ability to impart a driving desire to know into a character. So when an evil character who cannot comprehend good is on the receiving end of kindness, love, or mercy, she will get an insistent and annoying urge to know just why the hero and his cadre have done such an inexplicable thing. There's no way this Worthy Opponent would do something as stupid as save or help an enemy, she'll reason. She'll assume he's being The Chess Master and is trying to manipulate her, perhaps foolishly expecting her to feel she "owes him one."
So it eats away at her. She'll "study" good to try and understand how the hero will turn such an unfathomably idiotic act to his benefit. As the obsession grows, she'll probably spy on the hero and slowly develop a bit of a crush. She'll try getting close to him and understanding his actions by donning a disguise and doing minor good things, only to discover to her horror that Good Feels Good and she's Becoming the Mask, until eventually she does a HeelFace Turn.
This trope can exist between cultures as well as people of different morality. When people from two different cultures meet, a character from one culture may grow fascinated with the other over a small trinket, casual observation, or snippet of info. As he learns more the fascination grows, giving him a frame of reference with which to compare his own culture. This usually results in him realizing he's unhappy in his own culture, and leads to him defecting. Don't expect everyone on either side to be too thrilled about this.
Compare Grew Beyond Their Programming.
- In The Cartoon History of the Universe, a pagan Roman couple in the arena watch with fascination as a Christian martyr enthusiastically welcomes death by lion ("C'mon! What are you waiting for?"):
Pagan Man: Man, how do they do that?
Pagan Woman: Must... find... out...
- This happens all the time in Chick Tracts. A la "Who is Jesus? Tell me more!" and a few panels later they're crying and begging for forgiveness.
- In the Pony POV Series Dark World Arc, this triggers Twilight Tragedy's HeelFace Turn. She sees Apple Pie laugh at one of Discord's jokes despite said joke being about a horrible tragedy that had just been inflicted upon the poor filly. Tragedy is incapable of figuring out why, and her curiosity slowly overwhelms her. This also causes her to become curious about other things, like why she can't remember something Liarjack can. Being told what happened in Old Avalon during the Final Battle with Queen Cadence begins to trigger old memories buried for over a thousand years. When she finally talks to Apple Pie under the guise of an Earth Pony filly named Half Light Dawn, she finds herself asking other questions about various things that peak her curiosity about Apple Pie's family, gradually undermining her own beliefs on tragedy and other things. This results in a Villainous BSoD that causes her to retreat into her mind and confront herself, finally managing, with the help of Cadence's spirit (or her subconscious appearing to be her), she finally performs a HeelFace Turn.
- Cassandra Cain in Angel Of The Bat is said to have had some knowledge of Jesus and Christianity since she was a child living on the streets, but only becomes really interested after she rescues a priest being mugged and takes note of the way he almost immediately forgives his attackers. His philosophy sets her on the path that ultimate leads to her spirituality and Catholicism.
- In The Nightmare Before Christmas, Jack Skellington is deathly bored with running Halloween, so when he accidentally winds up in Christmasland he becomes morbidly curious as to how Christmas "works". Facing Blue and Orange Morality, he conducts experiments trying to measure the marigolds to quantify merriment, deduce generosity, and distill happiness. Eventually he embraces his image of the concept so thoroughly he tries to save Santa the hassle of running Christmas. It goes Horribly Wrong. In other words, this trope is deconstructed. Also, one should note that unlike most trope examples, Jack isn't evil.
- John Preston in Equilibrium is an interesting case. He was a loyal member of the Tetragrammaton, but he understands how people who aren't on emotion suppressants act, sort of intuiting emotion. After meeting a resistance member who reminded him of his dead wife, and killing his partner for going off the emotion inhibiting drugs, he accidentally-ish broke the morning vial emotion suppressants. Hello emotion! He later finds out that his son has been off the meds since Preston's wife's execution and has been successfully hiding it from even his own father. Then again, Preston didn't know his wife was off the meds too until too late.
- In Death Takes a Holiday, Death, while on his holiday in the land of mortals, ends up loving the human race, and the fact that they get to feel love, joy, and anger whenever they want, makes him understand why they fear him so and make him want to be a part of it. However, he must go back to continue his duty as The Grim Reaper.
- In Power Rangers Mystic Force, Itassis wonders how the Power Rangers keep beating the Ten Terrors, as the Terrors are more powerful than the Rangers are. Being more of a Anti-Villain than the others, she goes to the Rangers and asks them their secret. They answer "courage", and she eventually abandons the Terrors to learn more.
- This is a central mechanic for the True Fae in Changeling: The Lost. As primordial chaotic beings, they can't understand human things like altruism or love; they just view them as passing fancies to be tossed aside when convenient rather than defining forces. In trying to understand these bedrocks of humanity, they become human, cutting themselves off from their fae memories and a good chunk of the powers. Of course, in most cases, that only lasts as long as they don't start getting curious about fae existence...
- The mechanic, but not the trope, is inverted in its spiritual ancestor, Changeling: The Dreaming, where delving into fae lore and power causes one to become less human and more fae but this is unquestionably a Bad Thing, as humanity is the natural state and the dream is the corrupting influence.
- Teen Titans takes this for a much quicker spin than most. During Starfire's introduction, Robin is nice to her, and she is (understandably?) confused. He explains, and she claims the closest word her people have is "weak". Cue the middle of the episode, and she's seen the light.
- Steven Universe:
- Peridot starts to lean toward the Crystal Gems when she felt compassion for the first time while on Earth. She gets more curious on how much she can care for others and ends up experiencing more of what Earth has to offer. This (along with a heated confrontation with her boss) causes her to switch to Steven's side.
- Steven's own Missing Mom, Rose Quartz, had been said to have fallen in love with Earth life after she came to notice it around her and began exploring it out of curiosity. This becomes even more significant after the reveal that "Rose Quartz" was originally Pink Diamond, who first came to Earth as an Evil Overlord wannabe seeking to colonize the planet at first.
- Many colonization efforts in early America went this route:
- 17th century England was a generally lousy place to live, with ridiculous social stratification, an incredibly corrupt legal system, and extremely unsanitary living conditions. As a result, a major problem with early American settlements was that colonists (many of whom had come from debtor prisons) were working for corrupt, incompetent officials who had no idea how to run a colony. Meanwhile, the Indians who lived a few miles away were doing just fine even though they didn't have the "advantage" of brutal flogging for minor offenses. Those who learned how the Indians did it quickly realized that it was a vast improvement over their current way of life and promptly left.
- One particular element of this is that Native American cultures were far more egalitarian than their European equivalents, so what few women came to the New World were much more likely to ditch than the men were. It was this that ultimately caused arriving European settlers to lose their curiosity, as colonial authorities quickly concluded that the women were being "kidnapped" and made sure that any they "rescued" stuck to this narrative. Sadly, it was centuries before this interpretation of events was given any serious scrutiny, and guess who suffered in the meantime?
- Even after this, African slaves still made a run for Indian communities, for the obvious reason that being a slave sucked and they weren't all that quick to believe that Massa was telling the truth about Indians being savages, since Massa himself was a complete asshole. This is most famously the origin of the Black Seminoles. It should be noted that one of the big advantages in expanding the American frontier is that the bigger America got, the harder it was for slaves to run away to Indian tribes and become nearly unfindable. The fact that their captors would've also referred to the slaves' own freeborn African ancestors as "savages" probably also gave would-be runaways an entirely-different impression of what that word connoted. This also explains how so many current African Americans can find Indian ancestry in their lineage.
- This can also happen regarding religion, but not quite as easily as is sometimes portrayed. Also works in reverse (inversion?), where a person investigates their religion trying to answer their questions and concerns about it, and end up leaving the religion altogether; sometimes for another religion, a more personal, toned-down version of their previous one, even outright agnosticism or atheism. This is why many believers-turned-atheists claim that the easiest way to lose one's religion is to read one's holy text cover-to-cover without a middleman interpreting it. Naturally, there's plenty of people who do this on a daily basis and still retain their faith, so the argument is only valid for some people.
More generally, sometimes when extremist people with Black and White Insanity discover that The Enemy is not the Cult Of Pure Evil they had it hyped as in their mind, they assume that the side they were previously on is Completely Wrong and switch to an equally extreme position on the opposite side. It happens between religion and atheism, between different religions, between political factions, etc., anywhere there are two extreme factions bitterly opposing each other. Instead of reaching a more sane conclusion, sometimes their response to seeing a strong counterexample to their previous prejudices is to just say "GASP! EVERYTHING I'VE EVER KNOWN IS A LIE!!" and rubberband to the opposite extreme position.
- The scientific method and rational thought in general may be seen as calculated attempts to promote this kind of transition. They are founded on the notion that you should learn about the world by questioning, studying and testing it directly (in order to satisfy curiosity) and then use this evidence to update your beliefs and inform your decisions (conversion). Curiosity and doubt are sanctified as the more you learn, the more accurate your beliefs can be and the more readily you can achieve your goals.