Most people are aware that Evil Is Not a Toy, but there are a few that will go through the elaborate Summoning Ritual anyway and end up becoming a host for some demon or other, but in a few settings, making a deliberate Deal with the Devil isn't necessary for the demon to take control. The demon only needs a victim with the right (or wrong) mindset.
More specifically, this is the idea that being an evil person leaves you vulnerable to the influence of evil beings. There may be specific types of demons who seek out hosts who are guilty of specific crimes, or it's simply that people who are evil like themselves are less able or willing to resist the possession. This trope can also be used as a metaphor for crossing the Moral Event Horizon, where the author is basically saying "people who do these things are no longer human", in a literal Demonization of the act and those who commit it.
- Asshole Victim, for bad people meeting bad fates in general.
- Evil Makes You Ugly and Evil Makes You Monstrous, where an evil person's body is transformed rather than hijacked.
- Victim-Blaming for when people are blamed for the bad fates they suffer in general.
- Morgana Trace of Wheatley and Hemphill's Mars confronts her shipmates about their drunken behavior on Mars. "Drink a little nectar, see woolies and boogens. Drink more nectar, and the boogens own you." She promptly smashes the nectar still.
- Exploited in the Spanish black comedy El Día de la Bestia (The Day of the Beast). The main character, a priest, has a crazy scheme to save the world: to commit as much sin as possible, so that he can sell his soul to the devil in exchange for learning the birthplace of the Antichrist so the priest can kill it before it dooms mankind.
- Played for laughs in the film Idle Hands, which takes the phrase "Idle hands are the Devil's playthings" literally and causes the hand of a boy who never does anything to become possessed.
- In Jennifer's Body, her not being a virgin when being ritually sacrificed by Low Shoulder causes Jennifer Check to become demonically possessed.
- In The Divine Comedy, the second-to-last section of the innermost circle of Hell is home to those who betrayed their guests. Those who commit this sin get sent to Hell immediately upon committing it as their soul is displaced from their body by a demon.
- Michael Bentine, in one of his books on the paranormal, discusses the case of a publican who discovered he could predict the winners of horseraces. This publican also suffered from the occupational hazard of being an alcoholic. A psychic medium divined that he was possessed and exorcised him: the alcoholism went as did the ability to predict race winners. But the formerly possessed man did nothing to give thanks for his deliverance and regretted losing the ability to win big money on horses: sure enough the ability to predict winners returned along with the destructive drinking. Bentine notes that having effectively invited the possessing spirit back, nothing could save him this time and he ended up dying a lonely insane death.
- Not demonic possession, but in Jinx High the villain can't Grand Theft Me the next generation until that person can be morally corrupted.
- In A Hat Full of Sky, apprentice witch Tiffany Aching makes an error based on inexperience and a certain vanity. Untutored as to the pitfalls, she treats astral travel and going out of body as unremarkable and neglects to take safety precautions to prevent anything else from getting in while the back door is open and unlocked. She pops out of her body to check herself out, as if she is looking at herself in a full-length mirror; whilst checking her appearance, the possessing spirit called the Hiver takes occupation of her body.
- In The Second Coming, what makes people vulnerable to demonic possession is Despair. (Utter despair is considered a sin in some versions of Christianity, because it's incompatible with believing that God can and will help even the most miserable.)
- In The Bible, Matthew 12 43:45 suggests that a demon, once expelled, may return to the person it possessed:
When the unclean spirit has gone out of a person, it passes through waterless places seeking rest, but finds none. Then it says, "I will return to my house from which I came." And when it comes, it finds the house empty, swept, and put in order. Then it goes and brings with it seven other spirits more evil than itself, and they enter and dwell there, and the last state of that person is worse than the first. So also will it be with this evil generation.
- Theologians and Christian thinkers have extrapolated from this that being the mere passive recipient of an exorcism is not enough: the subject needs, metaphorically, to install better locks on doors and windows and an adequate burglar alarm system. (i.e. to accept the Christian message and actively reform their life so as to prevent re-occupation by demonic forces).
- A truth in the Warhammer and Warhammer 40,000 universes. In fact, in the latter, rampant sin in the Eldar empire resulted in the birth of a new Chaos god: Slaanesh.
- In Warhammer Fantasy setting, eating the flesh of the dead will twist the cannibal into a ghoul.
- Using Dark Magic is only "safe" in tiny amounts, or on very sparing occasions. Any living thing using it regularly will be driven insane - the only question is "when". There is no "if".
- An additional danger is that many texts of Dark Magic are of shoddy quality due to poor preservation and being written by madmen. And in the Warhammer World, you do not want to miscast your spell because of this trope. Witches are hunted for a reason.
- Chapters 36 and 37 of the Touhou Project supplementary manga Forbidden Scrollery feature an umatsuki, a type of Youkai that takes the form a horse who can detach its head to possess its victims, and targets those who have mistreated their horses.
- Undertale: taking the No Mercy path and deliberately killing everyone possible leads Chara, now a demonic entity, to possess you. This leads to a couple of cutscenes where they move you on their own as well as the bad ending, where you have to agree to sell your soul to them if you want to play the game again. (Unless you manually reset it yourself.)
- In Until Dawn, people who commit cannibalism on the mountain are possessed by the spirit of the Wendigo, and transformed into monsters. When Hannah is forced to eat her dead twin sister to attempt to survive lost in a mine, she is possessed by Makkapitew, the strongest and most powerful Wendigo ever.
- Subverted in Grandia II: At first, it seems the people possessed by the pieces of Valmar are guilty of some vice, such as the wealthy trade magnate who becomes a gluttonous blob while his employees starve. Gradually, it comes to light that Valmar can possess anyone who possesses strong desire, such as a young girl's desire to make the people of her village happy, and can as easily infect the innocent and good as the false and wicked.
- Breath of Fire II: All the servants of the Big Bad were normal, relatively speaking, people that went to become an embodiment of one of the Seven Deadly Sins, allowing the villain to transform them into demons. For example the first servant, Augus the manager of the Coliseum Tournaments in Coursair, symbolized Lust, specifically Bloodlust. He rigged the match between Ryu and Kat with the objective of making Ryu torture and kill the Cat Girl in front of a live audience as a sacrifice to his God.