The I problem.
I is in my head, in my speech, and in my line of sight.
I separates me from you. I have to not be “I” to see you, to understand you, and to try to “be” you.
You are another I, and it’s the same for you as it is for me. Multiply that by the number of you(s) that you or I might encounter in our lifetimes, and the problem is obvious.