Anime villains rarely end the series on a high note. They are usually defeated by the protagonist by the end, even if it does take a few altercations to reach a defining outcome. The reasons that these villains keep losing can be traced to a few key mistakes that many of them continue to make.
No matter how bad or scary the villain is, they are liable to make these mistakes. From the well-known and overdone trope of the monologuing villain to the hubris that makes these villains continually underestimate their hero counterparts, there are basic mistakes anime villains keep making.
10 They Monologue When They Should Just Act
The most stereotypical folly made by villains not just in anime but across all genres and stories is the tendency to over-monologue. This helps the hero by functionally stalling the evil plan and giving the hero time to either come up with a solution or have their reinforcements get into place.
A notable example of this was when Dabi's speeches during the Paranormal Liberation arc left room for the hero to make a getaway. Another instance of this was when Dracula left himself open to Alucard's attack while speaking to a not-present Lisa.
9 They Play The Long Game When They Should Swiftly Execute Their Plan
The villains like to draw out their plans in anime, and this sometimes serves a tactical purpose, but many times it simply serves to amuse the villain. They enjoy the thrill of the chase or watching the innocent squirm.
In Demon Slayer, Muzan could have made quick work of Tanjiro and his family, but he left Nezuko a demon. In Naruto, Orochimaru could have taken Sasuke without having to destroy the village, and it likely would have been more successful had they done it that way. He would certainly still have had the use of his arms and been able to take Sasuke's body before he got too powerful.
8 The Villains Follow The Rules Too Often
While there are plenty of villains who will do underhanded things to win, there are also a bunch of villains who are too noble for their own good. They play by the rules, offering the hero a fair fight when taking the "any means necessary" route would have been better for their overall plot.
A prime example of this was when Joseph Joestar went up against the Pillar Man, Wamuu. Because Wamuu was so concerned with getting a fair fight, he gave Joseph time to get stronger, and that was a huge mistake on Wamuu's part.
7 They Want Their Heroes To Be "Interesting"
Fans have all heard a frenzied villain shout "omoshiroi," or "interesting," while fighting the hero at least once in an anime. These villains love the difficulty of the battle or the pain on the hero's face. Often this comes from a place of deep sadism.
Hisoka from Hunter X Hunter is one character who will let the hero live because he considers them interesting. In My Hero Academia, Toga's love for and interest in characters like Deku kept those heroes safe, at least for a time.
6 They Don't Know When To Stop
Sometimes, the villain just needs to learn when to quit while they are ahead. However, more often than not, they are not satisfied and they greedily keep coming back for more. This leaves them open to defeat.
Deidara of the Akatsuki learned his weakness the hard way when he sought so fervently to kill Sasuke, despite there not being a need to. The vampires of Castlevania are almost all guilty of this, as well. They push to conquer all of humanity when they could just stop at any point.
5 They Are Overly Cruel To Innocents
A villain can sometimes go unnoticed or uncared about if they are not too cruel. For instance, Gentle Criminal was let go because he did not pose a real danger to society, at least not in Deku's mind. Unfortunately, many villains can't help but leave a wake of destruction in their path.
Villains who are guilty of this include Eren Yaeger, a hero-turned-villain who helped cause The Great Rumbling, and Fire Lord Ozai, who wanted to conquer the entire world with fire and did not care who he killed to do so.
4 They Are Likewise Too Cruel To Their Allies
The real shot to the foot is when a villain antagonizes their allies, thinking those allies will blindly follow them despite the mistreatment. Azula is a culprit of this. She antagonized Mai and Ty Lee, and they did not hesitate to turn on her during the Boiling Rock arc. It was all downhill from there for Azula.
On a larger scale, Light was willing (and did) to throw anyone and everyone under the bus in Death Note. He killed at a whim, and he did not seem to care one way or the other. However, this all caught up to him in the end when he did not have any more reliable allies to count on, not even Ryuk.
3 They Are Overly Zealous In Their Beliefs
Some villains get so wrapped up in their ideology that they cannot see the path in front of them. Returning to the example of Light Yagami, he not only let the Death Note corrupt him to the point of being a megalomaniac, but he also let it drive him into the ground.
Furthermore, zealots like Pain (also known as Nagato), destroyed entire villages for their ideals only to have to come to terms with the fact they were mistaken when someone finally gets through to them.
2 They Are Often Too Paranoid Or Obsessive
A one-track mind leads to putting all of one's eggs in one basket. Whether it be over another character, an ideal, or a powerful object or ability, some villains cannot see another way than the one straight ahead of them. This inflexibility is dangerous.
Muzan might have saved himself some trouble had he left Tanjiro's family alone and left them in the dark about the existence of demons. Perhaps, if Orochimaru had not been so dead set on having an Uchiha, he could have saved himself (and everyone else) a lot of grief. Himiko Toga's obsessions make her weak at times, as well.
1 They Underestimate The Heroes
The most common reason a villain loses, especially when it comes to the final battle, is because the villain is too sure of himself and thinks the hero too weak to matter. Often, this is bolstered by the villain's wins earlier in the series.
There is no better nor any more hilarious example than that of Saitama of One-Punch Man. His origin story is underwhelming, his character design is unassuming, and his villains are always underpowered, which is why he is almost always able to beat them in one punch.