Keeping the audience on its toes with daring storylines and shocking plot twists was a key part of what made The Vampire Diaries so popular. Some of the best storylines were a result of shocking plot twists that left the audience stunned, leading the show and the characters in a fascinating direction.
While the vampire-centric show managed to surprise its fans most times, some plot twists were easy to guess. The show's reliance on recurring tropes for many storylines was a major reason why it became predictable, and blatant foreshadowing of certain things also contributed to fans figuring out plot twists before they happened.
Elena Becoming A Vampire
After seasons of fighting to keep her humanity, Elena finally became a vampire in season 4. The season 3 finale, which led to her death and transformation, was one of the best of the series. It also had a nostalgic element to it with the reveal of the accident that killed Elena's parents running concurrently with Elena's death in the same place.
While the audience might not have guessed the exact moment Elena would become a vampire, they knew it was bound to happen sometime on the show. Besides the fact that she was surrounded by vampires and dating one of them, the frequent use of vampire blood to treat serious injuries and Elena constantly being in mortal danger were all recipes for her inevitable transition.
Single Serve Cure
The Vampire Diaries introduced the cure for vampirism through the hunters' storyline. The cure was originally created by the witch Qetsiyah for Silas, but it fell into several hands before it was eventually force-fed to Katherine by Elena. The biggest catch was that whoever took it would become mortal and their blood would become the cure. However, a single syringe of blood would remove the cure entirely from their body.
On a show whose primary focus was vampires, it seemed improbable to have the cure for vampirism be easily accessible so any of them could take it and be cured. Not only that but the complex story of how the cure came to exist promised even more complicated rules for its use.
Evil Elena
Devastated by Jeremy's death, Elena became overwhelmed with grief over every family member she'd lost. Damon told her to turn off her humanity when he could see that she wasn't coping and she complied. After that, she basically became Katherine 2.0, which was a far cry from her normally good-natured personality.
Elena as a human and as a vampire with her humanity on was still a good person, so the contrast with her humanity-off vampire persona wasn't surprising. The show had already shown how ruthless a vampire without humanity could be through Ripper Stefan back in season 3, so this ugly side of Elena was expected as soon as she flipped the switch.
Klaus Not Dying
In addition to all vampires being sired from an original, the show added the twist that if an original was killed then every vampire sired by them would die too. Before they discovered that, the Mystic Falls gang had tried to kill Klaus, but now realized they couldn't until they found out if he was the original they were sired from.
So, when Klaus was supposedly killed at the end of season 3, fans knew there had to be a loophole because there was no way the show would kill off all the vampires who were the majority of the main characters. Later, it was revealed that Bonnie did a little switcheroo and saved Klaus.
Matt Not Dying
When her humanity was off, Elena became a ruthless vampire, feeding on humans without remorse until Matt offered himself for her to feed on so she wouldn't hurt innocent humans. When she went too far, Damon threatened to snap Matt's neck if she didn't stop and flip the switch. She called his bluff and Damon went ahead and did it, only to reveal afterward that Matt was wearing the Gilbert ring all along and wasn't really dead.
Stefan's half-hearted attempt to stop him from killing Matt was a dead giveaway that there had to be a catch to Damon's threat. As the most moral of the brothers, Stefan would have made a better effort to stop him from killing Matt. Besides that, Damon had pulled a similar move before when he snapped Jeremy's neck after Elena rejected him—so it was easy to guess that the show could take that route to save Matt.
Elijah Betraying Elena
Elijah and Elena had a deal to get rid of Klaus once and for all. Once the others did their part, Elijah was supposed to deliver the final blow and kill his brother. But when the moment came, he didn't follow through and instead saved his brother.
While he was human, Elijah was a noble and loyal brother and becoming a vampire heightened his sense of duty towards his family. It was the basis for his vendetta against Klaus, whom he believed had killed their siblings. Based on that, his betrayal of Elena the minute he heard he had a chance to save the rest of his family wasn't surprising at all. Whether he would have gone through with killing his brother if he didn't have leverage, however, is another question altogether.
Big Bad Malachai
From his first appearance, Malachi—mostly referred to as Kai—showed he was manipulative and didn't hesitate to betray anyone else to serve his own interests. When he merged with Luke and killed him, Kai gained some of his empathy and claimed to have changed. For a while, he tried to be helpful and redeem himself but he eventually reverted to his old, evil ways and killed his twin, Jo, on her wedding day.
The other characters didn't believe Kai when he said he'd changed, despite everything he did to show it. While he might have gone on a redemption journey for a while, it was only a matter of time before he went back to being one of the most powerful villains on The Vampire Diaries. Especially because the reason for his change of heartfelt a little flimsy and wasn't likely to hold out for long.
Several Character Resurrections
One of the most recurring tropes on The Vampire Diaries was people coming back from the dead. Almost every main character died at least once and came back from the dead so much that there are even memes poking fun at the plot.
With so much dying and subsequent resurrection on the show, death became meaningless in most cases. While there were some deaths that stuck and broke fan's hearts, like Jenna's, others didn't have as much of an impact as it was obvious the show would find a way to bring them back, especially once the concept of resurrection was introduced.
Elena Taking The Cure
When Bonnie returned from the 1994 prison world, she brought the cure back with her. Elena took it and became human again and Damon planned to take it from her so they'd live the rest of their lives together as humans, but Kai cast the sleeping curse on her before he could.
Before she became a vampire, Elena was determined to keep her humanity and after she turned, she didn't fully embrace the vampire life for a while. So once a cure for vampirism was mentioned in season 4, the audience knew she would definitely take it. Since she'd only been a vampire for a couple of years, she wasn't in the same danger Katherine was of aging rapidly and dying and without that risk, there was no reason why she wouldn't want to take it.
Stefan's Death
During the series finale, Stefan and Damon faced off with Katherine, leading to Stefan tricking Damon and injecting him with the cure from his blood, before sacrificing his life to send Katherine back to hell.
Although Stefan's death felt unfair for some, fans saw it coming even before the final season began. It was his nature to sacrifice himself for others and since the story was his from the pilot, it was only fitting that it ends with his death.