Has anyone ever told you they understood you and then did something that someone who understood you never would?
You feel they not only don’t understand you, they think they did, which they don’t, and told you they did, which was wrong.
You write off that person as not understanding you and therefore not worth listening to or following. You might not even consider them worth your time to help them understand you. What’s the point if they think they do when they don’t? You could easily waste a lot of time with someone like that and get nowhere.
Now think of people you think you understand. Is it possible you sometimes think you understand someone when you don’t? If so, could people be writing you off?
If you think you actually understand everyone you think you do, how do you know you understand them? Might they have just given up on you?
Have you ever thought in a conversation “Why is this person repeating themselves so much to me? Don’t they get that I understand? If they would just talk less and listen more they’d understand me and see that my way of looking at things makes more sense”? If so, that person didn’t feel understood.
I’ve found the best way to know if you understand someone is to confirm with them. Very astute and observant people might figure others out from their behavior, but relying only on behavior keeps you from a more potent way to confirm—to ask for confirmation. Getting confirmation from someone is like getting a handshake. It feels better to have a solid, firm handshake and it feels good to have a solid, firm mutual understanding with someone you work with. Not confirming your understanding with someone is, to me, like not shaking someone’s hand.

The understanding handshake

The understanding handshake is my mental model to avoid misunderstanding someone when I think I understand them.
When someone shares something important with me, I think of it like they extended their hand to me for a handshake. As rude as I would consider it not to meet their handshake is as counterproductive to a relationship I would consider not meeting their opening up to me with confirmation that I understand. Usually that’s as simple as repeating your understanding and letting them correct you if you understood it wrong: “You say you don’t like your boss?” They’ll likely agree, correct you, or elaborate.
It may look pedantic when written, but in conversation it feels to the other person like you are putting effort in to understand them and gives them a chance to increase your understanding. If feels to them like you care, like you’re putting their interests before yours. It takes almost no time when your understanding was accurate. When your understanding was inaccurate, it takes more time in the moment, but saves you from the disaster of trying to influence someone who already gave up on you.