Sailor Moon is a superheroine who is also destined to become Queen of the Earth, but Usagi Tsukino is only human, even if she is also a Moon Princess. Usagi certainly has her bad habits, whether it's her poor grades or not always being able to save the day. Because of this, she does have her fair share of failures.
Of course, plenty of the times she messes up are not necessarily her fault, especially when actual villains are to blame. However, there are still times when she could have changed the outcome of a situation by paying more attention and remembering that she has powers.
10 She Keeps Getting Drunk At Parties
Accidentally getting drunk at a party once could be seen as an isolated incident, but this happens to Usagi on multiple occasions. While attending a party for international students, Usagi gets scared because of her poor English skills and accidentally gets drunk on what she thinks is juice.
To add to the irony, it turned out that Mamoru's friends actually spoke decent enough Japanese to talk to her. Fortunately, one of the students thought her drunken rambling about pudding was very insightful.
9 She Never Learned To Write In Kanji
Usagi saves the world from a second Ice Age and is recognized as the Earth's rightful Queen. After this, it would be assumed that she would mature out of her childish bad habits, especially since she seems to have become functionally immortal and have all the time in the world. While this initially appeared to be the case, Usagi's original personality occasionally shone through. It turns out that even as Neo Queen Serenity, she still cannot write in kanji, as seen in a letter she writes for Chibiusa during her second return to the past.
8 Villains Keep Finding Out Her Secret Identity
Throughout Sailor Moon, it seems to be an unspoken rule that nobody can directly recognize Usagi as Sailor Moon. Unfortunately, quite a few villains do eventually learn her secret identity, like Jadeite and Nephrite in the first series or Sailor Aluminum Siren and Sailor Lead Crow in the fifth series, among others.
Fortunately, they usually conveniently die, often at the hands of the other villains, before they get to act on it. Added to that, quite a few civilian characters are able to figure out her identity, too. In the manga, even Motoki eventually discovers that the girls are the Sailor Scouts.
7 She Handed The Holy Grail Over To The Bad Guys
Usagi can be a little too trusting, even when it comes to villains. This is especially seen when she gives the Holy Grail to Hotaru thinking that it will save her life. Unfortunately, she's being manipulated by Mistress Nine, who is hoping to summon Pharaoh 90.
That said, having some trust in Hotaru did turn out to be a good thing in the end, since her alter-ego Sailor Saturn is needed to take down Pharaoh 90.
6 She Wasn't Able To Free The Sailor Animamates
In the original Sailor Moon manga, Sailor Galaxia's minions, the Sailor Animamates, were counterfeit Sailor Scouts who murdered the real Sailor Scouts of their planets and took their place. The '90s anime cut out the middleman and implied they actually were real Sailor Scouts under Galaxia's control. This was shown when Sailor Moon was able to use her healing powers to remove one of Sailor Tin Nyanko's bracelets.
Unfortunately, Sailor Tin Nyanko was soon driven mad by a desire to be both good and evil, and eventually was killed by Galaxia herself. This suggests that Sailor Moon could have used her powers to save them from Galaxia's control all this time.
5 She Wasn't Able To Save Nephrite In Time
In the '90s anime, love began to have a transformative effect on the villain Nephrite, who developed feelings for Usagi's friend, Naru, after initially mistaking her for Sailor Moon's alter-ego. Unfortunately, the envious Zoisite orchestrates his death, having Youma kidnap Naru in a plan that ultimately leaves Nephrite mortally wounded.
In the end, the Sailor Scouts may have been able to fight against Zoisite's Youma, but they weren't able to save Nephrite in time. He eventually dissolved into nothingness in Naru's arms.
4 She Wasn't Able To Save Saphir
Another sympathetic villain of the '90s Sailor Moon would end up being failed by the Sailor Scouts: Prince Demande's brother Saphir. After receiving a call from Petz, who was in love with Saphir, the girls decided to protect him while he tried to tell his brother about Wiseman's true colors.
Unfortunately, a blast from Wiseman ended up killing Saphir before their very eyes, causing the Sailor Scouts to have yet another friend lose her love right in front of their eyes.
3 She Could Have Prevented The Death Of Sailor Venus
During the final battle with the Dark Kingdom, Sailor Venus dies while saving Sailor Moon from an attack from underneath, causing her to get captured in her place. Sailor Venus ends up killing herself in a kamikaze attack.
While her friends were all willing to sacrifice their lives to protect her, Usagi could have been a little more proactive during the fight. The original English dub even pointed out that she probably could have saved her friend by using her tiara. Fortunately, thanks to the Silver Crystal, Minako eventually got a second chance at life after Queen Beryl's defeat.
2 She Destroyed The Moon Kingdom
In the live-action series, instead of having the Dark Kingdom be behind the fall of the Moon Kingdom, it was changed to have Princess Serenity be the one to have annihilated her world out of grief over Prince Endymion's death. Even as Usagi, she was shown to be able to reawaken as the vengeful princess and serve as a threat to the Earth.
And she indeed obliterated life on Earth as she promised, although, unlike the lost Moon Kingdom, the Silver Crystal was able to save everyone in the end.
1 She Left The World When It Needed Her Most (As Sailor Cosmos)
Sailor Cosmos is the ultimate form of Sailor Moon, although it's somewhat ambiguous if she really is the same person as Usagi or some alternate version of her. During a war with Chaos, after losing everyone she loved, Sailor Cosmos fled in the hope of manipulating Sailor Moon into destroying the Galaxy Cauldron.
Ultimately, Sailor Moon chose a different path and managed to save her friends and the galaxy, causing Sailor Cosmos to muse that Sailor Moon is the true Sailor Cosmos, and that she would strive to match Sailor Moon's courage.