How often have we looked at someone and put them into 'that box' only to find that it wasn't quite the right box? Or maybe, we hear a person’s voice on the phone and pictured what they looked like only to find they looked nothing like what we envisaged them to look like?
This is your brain going through an often subconscious process of putting people into categories so that we can deal with them according to those who we have previously met. Your brain thinks that it is looking after your own interests by doing so.
The same thing happens when we try to establish a rapport with someone, we make assumptions about them and try to find something that we have in common to talk about. Don’t do it, it doesn't work that way.
If you want to establish a rapport with someone, to stand alongside them, get to know something about the other person first. How do you do this, you ask them. How simple is that?
Instead, focus on them in their current situation, then find out how they got to where they are now, then you have all the information that you need to establish a rapport and to help them with whatever it is they want help with.
When we prejudge someone who we are meeting for the first time, it can lead us to prejudice, making incorrect assumptions that leads us to treat them differently than we normally would do.
The words we say are also important when getting to know a person. Rather than say "I understand", (because you often don't), say "This is what it was like for me".
Few people do things to upset others. I am sure that most of us do not do or say these things intentionally to put a barrier in the way. It is human nature to want to help each other.
Know that this stuff is going on subconsciously, for the most part any way.