Sometimes when you don’t understand something, it’s because you’re not ready for it yet. This can be particularly true of fiction and other narrative, but it can be true of almost everything.
Sometimes there are specific identifiable things you have to learn first. Sometimes you can go back and learn those things, and then the confusing thing will start to make more sense.
Sometimes it’s not a specific thing you don’t know. Sometimes it’s mostly just not being ready yet. Sometimes it’s just a matter of giving yourself time and experiencing more of life first. Some things that are incomprehensible at one point in your life start making sense when you revisit them later.
It’s worth keeping this in mind. You don’t have to do or understand everything all at once. It’s ok to give yourself time. Eg: If a book you think it’s important to read doesn’t make sense to you, it may be worth putting it aside for a few years and trying again later. A skill that seems impossible to acquire may become possible later. Or any number of other things.
Not everything is like that. Time doesn’t make everything make sense and it doesn’t make everything possible. (And people who say “you’ll understand when you’re older!” are almost always being inappropriately dismissive.) But it is true of a lot of things for a lot of people, and it is probably an experience you will have at some point.
Short version: Sometimes things that seem incomprehensible start to make sense as you gain more lived experience. It’s important to keep in mind that you don’t have to do everything all at once, and you don’t have to understand everything all at once. Some things take time, and that’s ok.