Did you ever realize that everything going on in your mind -- every thought, feeling, sensation, everything you are aware of -- is in fact happening only in your private internal world? Your thoughts appear only to you, and are not being heard by anyone else whatsoever. There is one physical world here on earth, but billions of different internal worlds. We are all in our own separate theaters, witnessing entirely different shows, and yet we behave as it we are in the same audience, watching the very same event we call life.
Why is it important to contemplate this truth? To meditate on this is liberating, because it implies that what we are personally living inside our heads is not real. We are aware of our thoughts, so in that sense they are real. And yet, our thoughts do not exist outside of our awareness. There is nowhere else where the thought that is appearing to you at this moment is actually occurring. Unlike the way we imagine it, our thoughts are not solid, like trees or rocks that exist outside of us in some tangible way. Certainly I have never seen a thought walk by me on the street. Where, how and if thoughts even exist within the body is not clear. That thoughts appear to our awareness, on a giant projection screen (to which we are the audience), is all we know.
source: https://www.psychologytoday.com/us/blog/inviting-monkey-tea/201308/why-our-thoughts-are-not-real