Have you ever noticed how we humans tend to make up stories without checking out the facts? We start doing this when we are very young. When we are very small, our brain is not fully developed to think through things logically, and so we draw conclusions about ourselves and the world around us that are not the truth. As adults, we don't realize we are carrying these false assumptions until we have an ah-ha moment and discover what we believe. Then we have the opportunity to change our faulty beliefs.
Even as an adult, I find myself making up stories about people based on my own beliefs. Perhaps I see a very rich person that I don't know at all. I might decide something about that person based on my own beliefs regarding rich people. Or, I decide what my partner is thinking about me based on the look on his face, or his tone. Most of the time, what he is thinking has nothing to do with me. It's important for us to observe what we are saying and believing about ourselves and others. To do this, I try to be aware of myself when I am feeling uneasy and starting to make up stuff. It is usually about what I think others are thinking about me, or about the way I am thinking about others.
Another good way to deal with our assumptions is to ask the other person if what we are thinking is true for them. This involves being somewhat vulnerable. I say, I am making up a story that you think... is this true? The other person will either validate what I am thinking or debunk it.
The most insidious stories are about myself. Stuff I decided about myself maybe even before I could talk. I decided that I was not good enough for my mother's love based on how my mother acted toward me. I thought if I could be perfect, then she would love me. It was futile, my mother didn't love me any more for my perfection. I learned much later that the way my mother behaved had nothing to do with me. She was unhappy and depressed in her life. But as a small child, everything was about me in my own mind. I was the center of the universe, and I took everything personally (which is what children naturally do)!
So here is another tip: remember that most things are not personal - we all have our own issues and problems and we all react. Let's not take the reactions of others personally, or blame our own reactions on those around us. Have fun with this! Be light with yourself and play the game of self-discovery.