I don't trust first person narrators.
In real life, a first person narrator is telling you about events they either went through or heard about. They're going to color it with their own priorities, opinions, and a flawed memory. If you can get the same story from many sources, you'll start to get a bigger picture of what might have actually happened, but humans aren't recording devices. We aren't wired to play back without interpretation to some degree or another.
In fiction, I think the hallmark of a good writer is if their first person narration is flawed. You're not supposed to get the full story with perfect detail and no wiggle room for interpretation. I can't trust your narrator explicitly, because they don't know everything. If they do, you're cheating.
Sure, sure, your narrator might be this amazing super human with psychic abilities or something. They might actually know everything going on. If that's how you want to do it, I'm not going to stop you. Write what you need to write. I'm just going to point out that if you want the power to get into everyone's head that badly, you might want to write in third person omniscient instead of first person.
When I decided to write Elemental in the first person, that's something I had to wrestle with. My character has all of these flaws, opinions, experiences, and pride that keep him from telling the whole truth. I know, of course, what really happened. I drew as much of that out as I could, but as I work on writing more about the world, the reader will be able to learn just how Agrad's experiences colored his narration. For example, he doesn't know Ysili's motivations, but eventually he can guess. Does that mean he put those guesses into his own story? In some cases yes, in others no. There are some things about Ysili that Agrad doesn't understand or approve of, and Agrad is very kind in his choice of words because he doesn't wish to speak ill of the dead.
It's one of the things I love about the Hollows series by Kim Harrison. Her first person narrator, Rachel Morgan, is a good person. She comes across as honest, kind, helpful, and moral. Even then her experiences, opinions, and priorities color what kind of story she wants to tell about everyone else in the story, and how she wants the reader to think of her. If Rachel's character was seen through someone else's point of view, how different would the story be? If the series was told by Ivy, or by Trent, what would the world look like?
When you chose your point of view for your story, think very carefully if you want to go with the intimacy of first person. It might be a more immersive experience, but it's an opportunity to color how your reader thinks of the world you're writing, and the story you want to tell. Don't force your first person narrator to always tell the absolute truth. Their lies or omissions may open up narrative possibilities and future stories you hadn't considered before.