Cecil and Beatrix : blinded by duty, blinded by illusions
When I first wanted to find echoes of FF4 in FF9, I totally neglected the Beatrix and Cecil parallel. And at first sight, they are totally different : he's an insecure young man, a promising but beginner dark knight captain, and she's an already accomplished paladin, a firm leader of her army of Amazons. He's dressed in black, destined to wear gold, white and blue, she will stay in white and red.
The thing is that plotwise there are very similar episodes in the two games : their countries, Baron and Alexandria are the warring nations gathering the crystals, they attack the pacifist Cleyra/Mysidia, there's the bombing of Lindblum/Damcyan, the defense of young summoner Garnet/Rydia, there's the siding with former enemies Freyja/Elder of Mysidia, and the assault on the worldly threat Giant of Babil / the Iifia Tree …
Thought they are different, Cecil and Beatrix play the same typical role of the righteous and faithful warrior who discovers very late that he serves evil. They have some similar reactions to the events. They even have a physical or rather graphic design resemblance : they are visually impaired.
On some versions of the FF4 menu portraits, Cecil's helmet has barely eyes, making the meaning of his name visible ( Cecil, from latin "caecus", blind). As for Beatrix, she has a blindfold to cover her missing eye. Is it a coincidence that this is the right eye that is missing, so that she can't see what is "right" and wrong at first ?
It is really convinient for the plot that they are "blind", and it makes the discovery of their mistakes and their change of sides all the more awaited and spectacular. However, if you can put this blindness down to naivety and a bit of cowardice for Cecil, you can't stop there when you look at the story of Beatrix who seems to be anything but a coward: she only has to discover her mistakes to admit them immediately without looking for excuses, and when it is necessary to take up arms to defend what is right, she has no hesitation.
In reality, in both cases, we have a complicated situation : the corrupt sovereign they serve was once quite just. I will play devil's advocate and ask the question: can you abandon someone you are devoted to, a person who has always acted well for years at the first misstep ? Furthermore, Cecil and Beatrix are swordsman and swordwoman, high-ranking officers in the army. Serving without asking justifications is their duty, and it is not their role to criticize royal decisions. When you ask the npcs in the castle, everyone is lost and there is no evidence accessible to Beatrix that the people of Burmecia did not seek to attack Alexandria first, nor to Cecil that nobody in Mysidia was plotting to use the water crystal against Baron.
It is rather the role of the advisors to worry about the sovereign's bad decisions, which is a problem when the advisors are in reality a three-headed snake in disguise and two evil jesters (multiple heads for even more duplicity!):
If they can no longer obey the sovereign, the code of honor would command Cecil and Beatrix no less than to resign from their positions … something which is not obvious when one holds oneself in charge of an army. The real difference between Cecil and Beatrix seems that the first is very surrounded by friends who encourage him to regain his rank and hold on, hoping that the king of Baron will not go too far in his war whims : Cecil thinks they depend on him being a dark knight just as he depends on them … while Beatrix seems desperately isolated in the middle of her Amazons whose boasting seems to inconvenience her more than anything else : her life is her role in the army, she feels she has no choice but to exists for it or "disappear" like her rival Steiner.
It is probably also an illusion on their part to believe themselves as an irreplaceable keystone of their kingdom's power, because once they have left their role as captain and general … the infernal machine of war continues in full swing ! Golbez takes Cecil's place at the head of the Red Wings, and Queen Brahne herself directs the war from her airship, the Red Rose.
For both Cecil and Beatrix, resigning would be a step into the unknown, a path hidden behind their own illusions. In either case, it is when they face the proof that they serve a demon that they are forced to make the leap of faith and go into rebellion : when they witness the distress of a child persecuted by their sovereign, a child who has committed no other crime than to be born with a special connection to the divinities.