Pets are nice, however, sometimes adopting a pet just doesn't work out, and that's where you get this trope: someone adopts a pet, but the pet either runs away and doesn't come back, or it needs to go away.
If the pet runs away, the reasons may vary on why it doesn't come back: maybe the pet refuses to come back because it dislikes its would-be owner(s) or found (a) better owner(s). Maybe the pet found a new home and the previous owner(s) think(s) it would be happier there. Maybe the humans searched very hard and failed to find the pet so they gave up. And maybe, they just didn't care about the pet enough to search for it.
If the pet has to leave, again, there are several possible reasons: maybe the person has another pet which it eats the species of or which eats its species or which just doesn't get along with the new pet. Maybe it's feral or was raised in the country and is too used to living outdoors. Maybe pets aren't allowed in the person's home or that person just doesn't have the time and/or resources to look after the pet. Maybe someone who lives with the owner is allergic, or the pet is having too many babies and neutering and segregation aren't options. Quite often, it's because the pet is too destructive and/or disobedient. Sometimes, if a previous pet ran away and/or was mistaken for dead and comes back, the new pet has to leave. If this is the case, they'll often explain this by having the two pets not get along or the owner(s) not being able to afford/have time for two pets, but other times, it's never explained why the owner(s) can't just have two pets.
It must be noted that sometimes in the "too destructive" or "they just don't get along" scenarios, characters frankly give up too soon: it can take weeks or even months for two pets to learn to get along but they can become best friends once they do, and with a lot of species, especially dogs, destructiveness and disobedience are just baby behaviors that they eventually outgrow.
Sometimes, this trope is reasonable if it's a person's first pet, especially if they're a kid or are a bit dim/naive/incompetent. Sometimes, however, it doesn't make much sense if the person is very experienced with animals: they're so experienced, so why are they suddenly having so much trouble with this one?!
Pets dying does not count, because unfortunately no pet is immortal (or not in real life, anyway). Nor does it count when the animal is wild, because there's a pretty good reason why wild animals would run away or have to leave, although feral versions of domesticated pets can count.
A note on Subversions and Double-Subversions: if a pet runs away or is sent away but does come back, this only counts as a subversion if the coming back happens in another installment (a sequel, a different episode that's not part of a multi-parter, the next book, etc). The reason for this is that "pet goes away and comes back" is a common scenario in and of itself, but the audience is less likely to expect the pet to come back if it happens a while later. On the other hand, if a pet comes back a while later but goes away again, this can count as a double-subversion.
Usually enforced because Status Quo Is God and adding a new pet to the cast would shake up the status quo too much. Compare Pet Baby Wild Animal. May overlap with Shoo the Dog. Contrast A Boy and His X. Also contrast Come Back, My Pet! and Tropey, Come Home for when a pet is sent away or runs away respectively, but does come back.
Note: If you're considering a pet adoption, please think through the responsibilities and learn the basics on how to care for the animal, introduce the newcomer to any existing pets, etc. to minimize the chance that this will happen to you.
- Played for drama in the PSA "Do Not Abandon Your Pet". A man loves his dog, but his girlfriend, who has recently moved in with him, does not, so he abandons the dog in the park. The dog remains there for months, crying.
- In "Wilson's Epic Journey", an ad for lottery tickets, Wilson the dog is lost. When he comes back, his owner has a cat and Wilson doesn't want to live with the cat (possibly because the cat is asleep in his basket) so he finds a new owner.
- Bagi, the Monster of Mighty Nature started as a cute pink kitten given to the boy Ryo Ishigami by his father. However, the kitten, named Bagi, soon displayed capabilites and intellect far beyond those of any ordinary housecat. Concerned for his son's safety, Ryo's father decides to remove Bagi from his home, but Bagi has already fled. Ryo and Bagi would reunite by chance many years later.
- Zigzagged in Arthur Christmas. A kid named Maria writes to Santa asking for a dog that looks like her friend's dog Bippo who ran away, but it's never specified if he returned. Furthermore, it's possible Maria was making Bippo up for a joke, as she claims that he's blue.
- In Finding Nemo, P. Sherman tries to give Nemo away to his irresponsible niece Darla, but he escapes before she can even take him home. At the end, Sherman's own fish (Bubbles, Bloat, Deb, Gurgle, and Gill), starfish (Peach) and shrimp (Jacques) escape.
- Open Season: Mr. Weenie the dog runs away from home and joins the wild animals. Subverted as he later comes back.
- Zigzagged in Snoopy, Come Home: It's revealed that Snoopy had a previous owner, Lila, and the two loved each other very much. But then her family moved and her parents "decided they just couldn't keep Snoopy" and returned him. Naturally, he was then adopted by Charlie Brown, but in the movie, Snoopy got a letter from Lila saying she was in the hospital and wanted to see him. He visits her, and after she gets better, she asks him if he would like to stay with her permanently. After a tearful goodbye to the rest of the Peanuts gang, he goes to move in with her... only to discover she owns a cat and her apartment has a "No Dogs Allowed" policy. Free of his obligations to her, he joyfully returns to Charlie Brown.
- In The Smurfs 2, this is discussed: Patrick had a parrot named Zeus as a little boy but was allergic and didn't realize, so his stepfather took it away, pretending he was allergic to avoid making Patrick sad.
- Shows up as a minor subplot in Cry Wilderness. Paul's father, a park ranger, finds some raccoon kits that were apparently abandoned by their mother, so he brings them back home to be pets for his son. At the very end, the mother raccoon comes back, and Paul realizes he needs to let his pets go away with her.
- Exaggerated in Cat Walk, where the cat protagonist keeps running away from or being unsuitable for his owners, until he finally gets a permanent owner.
- Diary of a Wimpy Kid:
- In "Dog Days", the Heffleys adopt a dog named Sweetie Pie, or Sweetie for short, however, he ends up being too annoying and gets given to Grandma.
- In "The Long Haul", the Heffleys win a pig. They keep him and at first he's fine, but then several books later, he escapes and they don't get him back (but he's fine).
- In The Girl The Dog And The Writer in Provence, one of Freja and Tobias's neighbors used to own two rabbits named Nina and Odette, but they ran away.
- In one of the Henry Huggins books, Henry gets two guppies, but they have too many babies. He sells them all because he can't tell if one is pregnant (guppies give live birth) and he can't keep two because he can't tell the males from the females.
- In all of the Magic Kitten books, Flame the magical kitten must turn into a lion and leave at the end of the book.
- In Martin's Mice, Martin the cat adopts a mouse named Drusilla and her eight babies named One, Two, Three, Four, Five, Six, Seven, and Eight. When the babies grow up, they go stir crazy and so Martin lets them move out before releasing Drusilla and her husband, Cuthbert. Then he ends up getting adopted as a pet by a woman from the city and runs away to get back to the farm (and learns how selfish he was to the mice in the process).
- In the short story "Too Many Rabbits" by Paul Jennings, a boy adopts a pregnant rabbit named Pinky. Pinky's babies have babies and so on, and when he tries to separate the bucks from the does, the bucks fight one another, so he ends up selling all the rabbits.
- In Warrior Cats, while there are plenty of happy house cats, and most examples of pets escaping their owners to live in the wild happen a considerably long time after the adoption, there are a few examples in the series where we see both the adoption and the escape:
- In Rising Storm, Cloudpaw is caught by the humans who'd been feeding him and is brought to a house near Wind Clan territory. They've had him barely a month when they open the door to see what he's meowing about (which turned out to be his uncle coming to rescue him), and he escapes.
- Sometime around the events of Hawkwing's Journey, Frecklewish was captured by humans and brought to live in an apartment building, several stories high. They lost their new cat not long after, when she escaped by jumping from their windowsill to a fire escape and then to a tree that she was able to climb down.
- In the Graystripe's Adventure manga, Graystripe is caught by humans while trying to free his Clanmates from captivity, and is adopted by a family. Although he lets them pet him, his feral nature means that he's never completely at ease, and he scratches the furniture and shreds a toy at least once. Once he's let outside and gets over all the noise and smells of the city, he runs away with another pet cat to find his Clan.
- In the Sky Clan and the Stranger manga, Leafstar and her kits are captured by an elderly woman. Her Clanmates come to rescue them, and they escape alongside the woman's other cat.
- Zigzagged in Star Trek: The Original Series: Uhura buys a little alien called a tribble but has to get rid of it because all tribbles multiply like crazy and are "born pregnant". The zigzagging comes from the fact that it's a bit unsure if tribbles are generally kept as pets. Cyrano Jones sells them, but it's often stated that they make bad pets.
- Played with in the children's song "The Cat Came Back". Old Mr. Johnson wants to get rid of his unwanted cat. The cat has different ideas.
- Sesame Street: In one episode, Big Bird finds a turtle named Seymour and tries to keep him, but he runs away and Gina says that Seymour probably belongs in the park.
- In "The Gink", the first episode of The Wubbulous World of Dr. Seuss, Eliza Jane wants to keep a Gink (a creature that is a cross between a Gunk and a skink) as a pet. Even though Ginks can be kept as pets (Horton makes a video guide on how to take care of them), they need a lot of attention and the Cat in the Hat sings a song about how she should get a different sort of pet. Eliza becomes too busy caring for her Gink to play with her friends and by the time that's all sorted out, the Gink gets homesick, so she puts him in the jungle but promises to visit him when possible.
- In Farmville, puppies (but not adult dogs) run away if you don't feed them. You can bring them back, but that costs real money and they can't come back of their own accord.
- Moshi Monsters:
- In the mission "Super Moshiversity Challenge", the player character's roommate Hermitty Ginger has a familiar named Penny who is a Mini Money (a little coin-like thing that is kept as a pet in this game). At the end of the mission, Penny gets given away to the player character.
- In the mission "Kick Some Asteroid", Wally the Asteroid Miner has an anthropomorphic soda (again, these are normal pets in the Moshi Monsters universe) named Fizzy as a pet, but Fizzy accidentally detonates some explosive gems, so he decides to live with the player character.
- In "The Curse of the Paw Wavin' Kitten", the pirates try to keep a cat named Tingaling, but they give her away because they (probably falsely) believe she is cursed.
- In the Little Princess episode "Can I Keep It?", Princess has a frog named Froggy who she raised from tadpole-hood. When he grows up, she puts him back in the pond because he's too loud at night.
- In Martha Speaks, a flashback reveals that when Helen was younger (somewhere between three and six), she had a goldfish named Goldie but put her in the lake to play, after which Goldie did not return.
- In the Milly, Molly episode "Beaky", Milly raises a duck named Beaky but when he grows up, she has to put him back in the pond because his poop makes too much of a mess (even though most people with pet ducks keep them outside).
- In an episode of My Little Pony: Friendship Is Magic, Spike adopts a baby phoenix named Peewee. Phoenixes can be kept as pets in this universe (Princess Celestia has one named Philomena) but in the next season, photos reveal that Spike put Peewee back with his parents.
- In "Beach Blanket Babies", Chas gives Chuckie sea monkeys as a pet, but Chuckie believes the sea monkeys are homesick, and decides to release them in the ocean when he and Tommy go to the beach.
- In "Spike Runs Away", Tommy's family adopts a poodle named Cuddles and then two gerbils named Tanya and Rupert and. Cuddles has to leave because she's mean to the babies, while Tanya and Rupert poop in the house, give birth to way Too Many Babies, and then eventually run away.
- In "Chuckie's Duckling", Chuckie tries to keep a duckling named Herbert. Ducks can be pets, but Chuckie doesn't have a pond, so he puts Herbert back with his family in the park.
- SpongeBob SquarePants:
- In "My Pretty Seahorse", Spongebob adopts a seahorse named Mystery. Seahorses can be kept as pets in the Spongebob universe, however, this one is feral, so she needs to be set free.
- In "Dumped", Gary runs away so Spongebob adopts two snails named Lary and Jary and a worm named Rex. Lary has to go because he's too aggressive and Rex runs away, but it's unknown what happens to Jary.
- In "A Pal for Gary", Spongebob adopts a pet named Puffy Fluffy, who runs away permanently. Just as well, because Puffy Fluffy kept trying to eat Gary.