The movie Tremors 2: Aftershocks features a memorable scene in which Burt Gummer (played by Michael Gross), having just discovered a heretofore unknown to Gummer fact about the life cycle of the animals he is trying to manage, indignantly complains “I feel I was denied… critical… NEED TO KNOW… INFORMATION.”
We’ve all been there, although perhaps not in quite the same circumstances as poor Gummer. So have many protagonists. After all, a poorly informed (deliberately or otherwise) protagonist is more easily led into entertainingly ill-advised action. Enjoy the following five works in which protagonists are afflicted with plot-facilitating ignorance.
The Reproductive System by John Sladek (1968)

Faced with impending bankruptcy due to declining sales, the board of the venerable Wompler company pivot from toys to arms. Exactly what role a doll company can fill in the military-industrial complex is unclear. However, as the board has always been fantastically ill-informed, they are not deterred by the fact that they do not know what they are doing.
The renamed Wompler Research Laboratories hires Calvin Potter to work under Dr. Smilax. Due diligence not being part of the corporate culture, nobody except Cal knows that the MIT that granted Cal his degree is not the prestigious Massachusetts Institute of Technology, but rather the less prestigious Miami Institute of Technocracy, or that Cal’s degree, Bachelor of Biophysics Arts, is unlike to be useful to Wompler. What’s worse: nobody at Wompler save Dr. Smilax himself suspects that Dr. Smilax is a mad genius whose research will surely doom humanity.
While the very real risk that humanity will be subjugated or exterminated by Smilax’s creations is arguably concerning, the novel does provide readers with a heartening message: because ignorance is no barrier to wealth, provided only that one attach oneself to the military-industrial teat, so too is manifest derangement no barrier to funding for mad scientists, provided that they find a sufficiently blinkered industrialist. Everyone wins! Except for all the dead people.
Day by Night by Tanith Lee (1980)

Why anyone would settle a desolate tide-locked world is a mystery. For the inhabitants of this particular desolate tide-locked world, why their ancestors chose this planet for their home is less important than the fact that the complex machinery on which their lives depend is beyond their ability to repair or maintain.
Cosseted in a palatial Residensia, tale-spinner Vitra was able to ignore the entropic doom facing her world. Now her Residensia is breaking down. Faced with begging for charity from other aristocrats or joining the poverty-stricken masses, Vitra boldly opts for a third option: frame fellow aristocrat Casrus for a crime and appropriate his property once he is convicted. This scheme worked perfectly in Vitra’s own fiction, so why shouldn’t it work in real life?
Yes, Vitra is trying to reuse the plot of a soap opera with which the masses are familiar. She does consider some of the obvious potential pitfalls in such a gambit. As it turns out, there are certain facts of which she is unaware, facts that are far more important than her bold scheme.
A Spell of Empire: The Horns of Tartarus by Michael Scott Rohan & Allan J. Scott (1992)

Left unemployed by the explosive results of his former employer’s research, apprentice alchemist Volker is happy to accept wine merchant Ulrich Tragelicht’s job offer. Volker joins a team whose members each possess both magical and musical talents… save for Ulrich himself, who knows magic but is tone-deaf.
The ostensible reason for Ulrich’s expedition to the Southern Empire is trade. Volker discovers that Ulrich’s true purpose is to confound malevolent cultists. It is a worthy cause (if only because, if successful, the cultists might doom the world). Therefore, when Ulrich is murdered, Volker steps in as leader. Too bad for Volker, his allies, and quite possibly the world, Ulrich died before he could explain just what his plan was.
Yes, this is a possibly-inspired-by-Warhammer-Fantasy-Roleplay novel in which we learn that the late Emperor Constans sounded suspiciously like Mario and Luigi from Super Mario Bros. In fact, I think it may be the only possibly-inspired-by-Warhammer-Fantasy-Roleplay novel in which we learn the late Emperor Constans sounded like Mario and Luigi.
Ansuz by Malene Sølvsten, translated by Adrienne Alair (2016)

Abandoned as a baby, Anna Sakarias has since been handed from foster home to foster home, scapegoated, bullied, and made a pariah. Were that not enough, she is plagued by terrible dreams. One might expect schoolmate Luna’s sudden insistence that Luna is Anna’s friend to be a welcome surprise. But Anna isn’t at all sure that she believes in Luna’s sudden volte-face.
Anna then discovers that Luna’s parents were Anna’s parent’s close friends. This is only one of many facts about which Anna finds she has been kept ignorant. For example, Anna owns a house in which she could have been living… if she’d known she owned it. Anna doesn’t know that she has magical powers; she doesn’t know that her dreams are visions! Most important of all: Anna doesn’t know that she is a potential threat to an other-dimensional queen… which is why even now assassins are hunting an ill-prepared Anna.
Luna’s parents thought Anna was safe with trustworthy people. That was a courageous belief, given that almost all of the adults in this book1 appear to be criminally negligent or actively hostile towards Anna. I would not trust most of the adults in this book to peel a banana without supervision, let alone raise a baby on whom the fate of worlds depends. The teens are not much better: Anna, although aware that a serial killer is stalking redheads in her region, does not mention to anyone her black hair comes from a bottle and her natural colour is red.
Daemons of the Shadow Realm by Hiromu Arakawa (2021 onward)

Yuru lives in a bucolic mountain village. While his parents fled years ago and he is functionally an orphan, he does have the company of his beloved sister Asa… in a way, as she is imprisoned in the village. Of the world beyond the village’s border, Yuru has little knowledge or interest. As Yuru discovers, the reverse is not true. There are those outside the village who know of and are keenly interested in Yuru and Asa.
The sudden incursion of hostiles into the village brings revelation. The most obvious fact? That the invaders are gleefully homicidal. Yuru soon learns that he can command demons, that he has been lied to his whole life, and the person he thought was Asa was only an imposter playing a role to keep Yuru from leaving the village. Why the ruse? Why are Yuru and Asa so important? To learn that, Yuru will have to venture into modern Japan, about which he knows nothing.
Manga fans may know Arakawa as the author of the life-affirming Silver Spoon agricultural coming-of-age manga. This is not that sort of manga. I am sure Silver Spoon fans would work that out by the time they reach the panel in which an extremely traumatized little girl watches her mother being gruesomely murdered… but perhaps a heads-up might be helpful (Fans of Arakawa’s Fullmetal Alchemist, on the other hand, will find just the sort of manga they expect.)
A protagonist’s ignorance of critical need-to-know information is a tremendously useful tool in any writer’s toolkit2. No surprise that the above works are only a very small sample of a very large pool of possible examples. It may be that I overlooked3 your favourites. If so, please mention them in comments below.