The Vampire Diaries was filled with characters who at one point or another made bad decisions that had catastrophic consequences. Usually, these decisions were made in acts of impulsivity, without much thought as to what the outcome would be.
While some of the characters' decisions weren't as bad as others, there were still many questionable judgement calls that left fans perplexed. Whether it was trusting the wrong people or making decisions based on selfish motivations, each character fell victim to making poor choices.
Jeremy: Trying To Become A Vampire
Throughout season 1 of The Vampire Diaries, Jeremy wasn't a particularly likable character due to his immaturity and selfish behavior, especially toward Elena. As a result, he made some wayward decisions and didn't take into other people's feelings, like in the season 1 finale "Founder's Day," when he tried to turn himself into a vampire.
Anna had given him a vial of her blood and tried to convince him to turn into a vampire so they could leave town together. Jeremy had initially been against the idea, but upon learning that Anna had been killed, he decided to drink her blood and then take a bottle of pills. He wasn't successful in his attempt, but the decision was a reckless one with little thought behind it.
Tyler: Trusting Jules
It has been debated that Tyler was Caroline's worst love interest in The Vampire Diaries, and his decision to trust Jules and thus betray Caroline was a good indicator of this. Jules, immediately upon her introduction to show, appeared to be an untrustworthy character, but Tyler fell victim to her persuasions and chose to trust her against the advice of his friends.
Tyler's faith in Jules led to an ugly confrontation when Jules and her boyfriend kidnapped Caroline and tortured her in "Daddy Issues," leaving Tyler helpless to intervene. Tyler did some appalling things throughout his time on the show, but his naivety in trusting a woman he barely knew over Caroline was truly one of the worst decisions he made.
Matt: Starting A Relationship With Rebekah
Matt was one of the few characters in The Vampire Diaries who was genuinely good, but this often left him open to being taken advantage of. While Rebekah seemed sincere in her intentions toward Matt, his choice to befriend her, let alone start a relationship with her, was out of character and a bad judgment call.
Matt was aware of the terrible things Rebekah had done, and knew some of these things involved his friends, but he fell for her anyway. Matt deserved better than Rebekah but continued with their warped relationship while aware that it would never work out. For a character who was so good-natured, he should have made better decisions when it came to his love life, e.g., steering clear of vampires.
Alaric: Trying To Avenge Isobel
When Alaric arrived in Mystic Falls, his intention was to find the person responsible for killing his wife, and this was an irrevocable decision that changed his life. Alaric's need for vengeance led to him to discovering the truth that she was never dead but had left him to be come a vampire.
While Alaric settled into his new life in Mystic Falls and made a family of sorts with Elena and Jeremy, terrible things happened to him as a result of uncovering the truth about Isobel. Not only was he heartbroken upon hearing of her deceit, but he also endured pain that he wouldn't have if he hadn't come to town, and it was clear that Isobel wasn't worthy of his love in the first place.
Bonnie: Turning To Dark Magic
Bonnie had a strong moral com and was considered the most powerful witch in The Vampire Diaries. She proved the enormity of her strength, usually by saving her friends. However, her power also led her astray and blinded her to the severity of her actions, such as in season 4 when she trusted Shane.
Shane used Bonnie for her magic to revive Silas, and Bonnie was a pawn in his warped plan to bring his wife and child back. Throughout this arc, Bonnie was warned on multiple occasions to stop using the magic that Shane was teaching her, but she followed through, and the results were catastrophic when Silas was revived. Bonnie was usually head-strong and independent, but her desire to learn more and help her friends clouded her judgement, especially in this instance.
Caroline: Turning Her Humanity Off
The arc that followed Liz's death was heartbreaking on many levels, and Caroline's grief made her act irrationally as she decided the only way to get through it would be to turn her humanity off. Despite Elena's protests, Caroline did it anyway in the episode "Let Her Go," and the decision led to a series of bad outcomes.
Considering that Caroline had seen the severe ramifications when Elena turned her humanity off in season 4, she should have put more thought into her decision before going through with it. While Caroline was without humanity, she did many dreadful things, most notably making Stefan her in her depravity and killing multiple people. All of it could have been avoided had she turned to a healthier outlet for her grief rather than make this choice that caused her so much more pain down the line.
Damon: Telling Elena To Turn Her Humanity Off
Damon did many terrible things in The Vampire Diaries, but due to his impulsivity, viewers can assume that a lot of his heinous actions didn't involve a lot of decision making. Yet in season 4's "Stand By Me," Damon bent the power of his and Elena's sire bond to his will, telling her to turn her humanity off.
While Damon was doing what he thought was the right thing to stop Elena feeling pain, the results of his decision were cataclysmic. Not only did Elena become reckless and dangerous without her humanity, but she also lost her connection to Damon. Damon was once more without her and was also partially responsible for the all the terrible things she did when devoid of humanity.
Stefan: Letting Katherine Back Into His Life
Disregarding the times when he turned his humanity off, Stefan was usually a measured and moral character in The Vampire Diaries, striving to do right. Yet when a seemingly repentant Katherine came back into his life in season 5, Stefan accepted her help, and he even slept with her in "The Cell."
Considering all the hell that Katherine had put Stefan through until this point, it was a terrible idea for him to let her in again, no matter how sincere she seemed. One of Stefan's best and worst traits is his empathy, and when it came to Katherine, it was clear that if Stefan gave her any inclination that he cared, it wouldn't end well. Stefan may have distanced himself in the end, but Katherine took advantage of his kindness, and it was a decision that Stefan should have known better than to make again.
Elena: Choosing To Erase Damon From Her Memory
Many sad things happened to Elena in The Vampire Diaries, and Damon's death at the end of season 5 was one of the worst. The experience proved to be too much for her to deal with, so she asked Alaric to erase any memory of Damon from her life.
With all of the grief Elena endured, it was understandable that she couldn't take anymore, but that doesn't mean this wasn't a selfish decision. While she did many questionable things, especially when her humanity was off, her decision here undermined her relationship with Damon and disregarded all the good times they had together. Things only got worse when Damon returned and Elena had no clue who he was. It was an ill-thought-out decision with ripple effects that touched everyone involved.