Although The 100 was wildly popular and featured some of the most interesting sci-fi twists in all of television during its run, it did have some issues. Despite all of the good bits, it wasn't always the most tightly written show, meaning that there were a number of plot holes throughout its history.
These range from things that don't make sense within the rules set by the show, inconsistent character moments, illogical science facts, and more. Fans of the show typically loved it so much that they were often fine with ignoring these details and just enjoying the drama that unfolded.
Becca's Lab Surviving
Becca Franko is as important to the story as anyone on the series. It was her work that caused the first nuclear apocalypse, she eventually helped form The Grounders, and she was the creator/face of A.L.I.E. It all started in her lab, which Raven and her friends eventually stumble upon.
This lab proved to be pivotal in figuring out ways to save the human race and doing experiments. However, it makes no sense that this was even possible. Most of the world was decimated by the nuclear apocalypse yet this lab somehow remained intact, fully functional, and pristine.
Technically, Bellamy Was Right
A major issue that even the most loyal of fans had with the final season of The 100 was the direction of Bellamy Blake. In seemingly one episode, he completely changed, turning on his friends for his newfound belief in the idea of transcendence.
Bellamy's belief in this concept led to Clarke having to kill him. While the audience mostly agreed with her decision since it saved Madi, at least temporarily, it's interesting to note that Bellamy was right. Transcendence was a real thing that the characters did in the end, so maybe they should've listened to him.
Nightblood Fights
The whole idea of The Grounders only being led by Nightbloods is a pretty cool one that helps make their leaders distinct. The problem is that the process they go through to figure out which Nightblood will be their leader doesn't really make any sense. Nightblood children are put together to fight against one another in the Conclave, with the winner ascending into leadership.
That's how Lexa got her spot and how Luna likely would have had she not left to avoid killing others. It's pointless to kill off so many Nightbloods if they're special. If the winner dies in combat or something like that soon after, there would be no Nightbloods left to replace them.
Grounders Speaking English
The Grounders should theoretically be able to speak English due to the time difference between the apocalypse and the start of the show (more on that later). Alas, when they're introduced, they don't seem to speak the language until Lincoln reveals that he understands Octavia.
The two go on to communicate often and Lincoln explained that only warriors were taught English. Of course, when it became convenient for the plot, almost every Grounder could suddenly speak and understand English regardless of their rank, position, or even age.
Basic Science Doesn't Line Up
A sci-fi show doesn't always have to be seeped in completely accurate science but it should get basic things right. Unfortunately, a lot of the scientific things about The 100 don't add up. It starts right from the very first episode, with things like the characters not noticing much of a difference on Earth.
Simply walking would take some getting used to due to gravity but they have no issue. There's also the fact that certain people are immune to radiation without any real explanation for how or why that happened.
Lexa's Blood
Lexa being a Nightblood is a huge part of her storyline and her overall character. It's what made her special, allowed her to compete to become the commander of The Grounders, and led to her appearance in some later episodes through The Flame.
That makes it especially odd when the audience gets to see her bleed at one point. Near the end of season 2, she shows up with blood on her face and it's red instead of the black color that it should be. It could be that it's someone else's blood but it doesn't seem that way. It's more likely that the Nightblood storyline hadn't been fleshed out yet.
Radioactive Animals Disappeared
One of the coolest scenes at the start of the show was when Clarke, Octavia, and a few others discovered a deer that seemingly had two faces. It was meant to be a sign of what the radiation levels on the planet had done to a lot of the living creatures.
While it's enough of an issue that it didn't seem to impact many humans, the bigger problem is that it's never really seen again. Other than the deer, some neon-looking butterflies, and a mutated gorilla in season 2, these animals or even regular-looking ones don't show up again.
97 Years Doesn't Add Up
As mentioned earlier, many of The Grounders didn't speak English, or at least that's how it was at the beginning of the show. The idea was that between the time of the first nuclear apocalypse and the 100 arriving on Earth, The Grounders built up their own lore and created a language.
The issue is that the 97 years between those events really isn't as long as it might seem. That's about three generations, maybe four at the most. It's more likely that they'd still speak English and that they wouldn't have such a long history of Nightbloods, commanders, and things like that.
Transcendence Is Just The City Of Light
The 100 wrapped with Raven and Octavia helping to prove that humans deserved the opportunity to transcend. This meant that they could evolve past their human forms and become part of a universal shared consciousness where they are at peace and never feel pain.
In theory, it might sound okay but this was literally what the characters fought so vehemently against in earlier seasons. A.L.I.E. spent nearly all of season 3 trying to get Clarke, her people, and everyone else to join the City of Light, which was almost identical to transcendence. Why was it something the characters were fine with at one time but not at another?