Pull out your phone and take a picture of something with it. View the image on your phone and then view the thing you took a picture of in real life. The camera image is obviously different, right? Cameras take images roughly the same way a human perceives vision. Light goes into a receptacle, that receptacle relays the information contained within the light to a processing unit, and then the processing unit then renders the information. What you see with your eyes is actually what your brain interprets you as seeing.
In that sense, even though the image quality in your camera is obviously inferior to what you see with your own eyes, even your own eyes aren't giving you the real thing. What you think is reality is just your perception of reality. When you view an image on your camera or phone, you're seeing another thing's perception of reality through your own reality lens.
That general principle extends beyond vision. Let's say you are contemplating an intensely polarized issue like gun control. Although there are nuanced views and middle-of-the-road compromises, we're not arguing from a standpoint of "gun ownership rights and regulations, go". We're arguing on the margins. The national conversation revolves around: should there be more or less regulation of gun ownership?
The issue is highly charged and complex. Various people are throwing various arguments, studies, and statistics at you and you're left to sort out what is right, what is wrong, and where to go from here. So what do you do? And how do you come down on the issue?
It takes a few things to establish an ideological position. The first is your perception of reality. What's going on? The second is your view on priorities. What's important? From there, you can craft your own idea of what reality should be like. That last part is ideology. There are poor people around me (perception). Being poor sucks (priority). Poor people shouldn't be poor (ideology). The process through which government bridges reality (the way things are) to ideology (the way things should be) is through politics.
The way this gets messy is when people don't view things the same way. There are an infinite number of vantage points. Some views get more light. Some have more a better view of the entire situation. Some views are from above. Some are from below. The way an urban elite Democrat views reality is vastly different from a rural working class Republican. In short, two people are looking at a photo and one sees a vase and the other sees a desk. It gets infinitely harder to come to an acceptable compromise when people can't even agree on what they see.
A lot of conflict in TV, books, and film is driven by the asymmetries that occur from two different viewpoints. In a romantic comedy, the lead character might view his/her love interest with a potential rival and interpret that wildly differently from what was actually going on (the love interest was just hugging their sibling). In a courtroom drama, the entire plot usually revolves around two people's recollection of what happened (the defendant's testimony versus the victim's).
The audience is privileged in that they usually get a much better vantage point than the characters. For example, we may know there's a serial killer lurking right behind that closed door at the end of a dimly lit hallway, but our plucky protagonist might not. Sometimes, the writer/filmmaker manipulates the audience with that assumption and turns it on its head in a staggering twist. Unfortunately real life doesn't work that way. We just get one vantage point. Our own. And in situations where more than one person is involved, it is almost always woefully inadequate to paint an accurate picture of what's actually going on. Each person has their own side to a story. But there's just one story.